[Docs] Restructure of Git Best Practices doc (qmk#7231)

* Add "Resynchronizing an Out-of-Sync Git Branch" doc

* Update (Git) Best Practices doc title and filename

* Rename Branch Resync doc

* fork Best Practices doc into multiple files

* Add the doc list to Git Best Practices doc

* Update sidebar

* Update internal references

* Update sidebar - add subsection

* Update Your Fork's Master page title

* title case on Git Best Practices main doc

* ... and in the Resynchronizing a Branch doc

* Please read Part 1

I worked really hard on this, okay?

* Please use branches, too.

* suggestions by mtei

* change note about adding multiple files

* note that the name given the remote repo is arbitrary

* suggestions by fauxpark

* Git Best Practices -> Best Git Practices

Reads more naturally.

* rephrase hint block regarding remote name

* rework the resynchronization instructions per mtei

* use hint boxes for reference to Part 1 doc

I may be addicted to hint boxes. I'm sorry fauxpark. 😢

* add some clarity about the upstream repo

* wordsmithing per mtei

* restyle the shell code blocks

Makes them more consistent to the other docs in this section.

docs/_summary.md

@@ -3,7 +3,10 @@
   * [Building Your First Firmware](newbs_building_firmware.md)
   * [Flashing Firmware](newbs_flashing.md)
   * [Testing and Debugging](newbs_testing_debugging.md)
-  * [Git Best Practices](newbs_best_practices.md)
+  * [Best Git Practices](newbs_git_best_practices.md)
+    * [Using Your Fork's Master](newbs_git_using_your_master_branch.md)
+    * [Resolving Merge Conflicts](newbs_git_resolving_merge_conflicts.md)
+    * [Resynchronizing a Branch](newbs_git_resynchronize_a_branch.md)
   * [Learning Resources](newbs_learn_more_resources.md)
 
 * [QMK Basics](README.md)

docs/newbs_git_best_practices.md

@@ -0,0 +1,16 @@
+# Best Git Practices for Working with QMK
+
+## Or, "How I Learned to Stop Worrying and Love Git."
+
+This section aims to instruct novices in the best ways to have a smooth experience in contributing to QMK. We will walk through the process of contributing to QMK, detailing some ways to make this task easier, and then later we'll break some things in order to teach you how to fix them.
+
+This section assumes a few things:
+
+1. You have a GitHub account, and have [forked the qmk_firmware repository](getting_started_github.md) to your account.
+2. You've set up both [your build environment](newbs_getting_started.md#set-up-your-environment) and [QMK](newbs_getting_started.md#set-up-qmk).
+
+---
+
+- Part 1: [Your Fork's Master: Update Often, Commit Never](newbs_git_using_your_master_branch.md)
+- Part 2: [Resolving Merge Conflicts](newbs_git_resolving_merge_conflicts.md)
+- Part 3: [Resynchronizing an Out-of-Sync Git Branch](newbs_git_resynchronize_a_branch.md)

docs/newbs_git_resolving_merge_conflicts.md

@@ -0,0 +1,79 @@
+# Resolving Merge Conflicts
+
+Sometimes when your work in a branch takes a long time to complete, changes that have been made by others conflict with changes you have made to your branch when you open a pull request. This is called a *merge conflict*, and is what happens when multiple people edit the same parts of the same files.
+
+?> This document builds upon the concepts detailed in [Your Fork's Master: Update Often, Commit Never](newbs_git_using_your_master_branch.md). If you are not familiar with that document, please read it first, then return here.
+
+## Rebasing Your Changes
+
+A *rebase* is Git's way of taking changes that were applied at one point in the commit history, reversing them, and then applying the same changes at another point. In the case of a merge conflict, you can rebase your branch to grab the changes that were made between when you created your branch and the present time.
+
+To start, run the following:
+
+```
+git fetch upstream
+git rev-list --left-right --count HEAD...upstream/master
+```
+
+The `git rev-list` command entered here returns the number of commits that differ between the current branch and QMK's master branch. We run `git fetch` first to make sure we have the refs that represent the current state of the upstream repo. The output of the `git rev-list` command entered returns two numbers:
+
+```
+$ git rev-list --left-right --count HEAD...upstream/master
+7       35
+```
+
+The first number represents the number of commits on the current branch since it was created, and the second number is the number of commits made to `upstream/master` since the current branch was created, and thus, the changes that are not recorded in the current branch.
+
+Now that the current states of both the current branch and the upstream repo are known, we can start a rebase operation:
+
+```
+git rebase upstream/master
+```
+
+This tells Git to undo the commits on the current branch, and then reapply them against QMK's master branch.
+
+```
+$ git rebase upstream/master
+First, rewinding head to replay your work on top of it...
+Applying: Commit #1
+Using index info to reconstruct a base tree...
+M       conflicting_file_1.txt
+Falling back to patching base and 3-way merge...
+Auto-merging conflicting_file_1.txt
+CONFLICT (content): Merge conflict in conflicting_file_1.txt
+error: Failed to merge in the changes.
+hint: Use 'git am --show-current-patch' to see the failed patch
+Patch failed at 0001 Commit #1
+
+Resolve all conflicts manually, mark them as resolved with
+"git add/rm <conflicted_files>", then run "git rebase --continue".
+You can instead skip this commit: run "git rebase --skip".
+To abort and get back to the state before "git rebase", run "git rebase --abort".
+```
+
+This tells us that we have a merge conflict, and gives the name of the file with the conflict. Open the conflicting file in your text editor, and somewhere in the file, you'll find something like this:
+
+```
+<<<<<<< HEAD
+<p>For help with any issues, email us at [email protected].</p>
+=======
+<p>Need help? Email [email protected].</p>
+>>>>>>> Commit #1
+```
+
+The line `<<<<<<< HEAD` marks the beginning of a merge conflict, and the `>>>>>>> Commit #1` line marks the end, with the conflicting sections separated by `=======`. The part on the `HEAD` side is from the QMK master version of the file, and the part marked with the commit message is from the current branch and commit.
+
+Because Git tracks *changes to files* rather than the contents of the files directly, if Git can't find the text that was in the file previous to the commit that was made, it won't know how to edit the file. Re-editing the file will solve the conflict. Make your changes, and then save the file.
+
+```
+<p>Need help? Email [email protected].</p>
+```
+
+Now run:
+
+```
+git add conflicting_file_1.txt
+git rebase --continue
+```
+
+Git logs the changes to the conflicting file, and continues applying the commits from our branch until it reaches the end.

docs/newbs_git_resynchronize_a_branch.md

@@ -0,0 +1,71 @@
+# Resynchronizing an Out-of-Sync Git Branch
+
+Suppose you have committed to your `master` branch, and now need to update your QMK repository. You could `git pull` QMK's `master` branch into your own, but GitHub will tell you that your commit is a number of commits ahead of `qmk:master`, which can create issues if you want to make a pull request to QMK.
+
+?> This document builds upon the concepts detailed in [Your Fork's Master: Update Often, Commit Never](newbs_git_using_your_master_branch.md). If you are not familiar with that document, please read it first, then return here.
+
+## Backing Up the Changes on Your Own Master Branch (Optional)
+
+No one wants to lose work if it can be helped. If you want to save the changes you've already made to your `master` branch, the simplest way to do so is to simply create a duplicate of your "dirty" `master` branch:
+
+```sh
+git branch old_master master
+```
+
+Now you have a branch named `old_master` that is a duplicate of your `master` branch.
+
+## Resynchronizing Your Branch
+
+Now it's time to resynchronize your `master` branch. For this step, you'll want to have QMK's repository configured as a remote in Git. To check your configured remotes, run `git remote -v`, which should return something similar to:
+
+```sh
+QMKuser ~/qmk_firmware (master)
+$ git remote -v
+origin  https://github.com/<your_username>/qmk_firmware.git (fetch)
+origin  https://github.com/<your_username>/qmk_firmware.git (push)
+upstream        https://github.com/qmk/qmk_firmware.git (fetch)
+upstream        https://github.com/qmk/qmk_firmware.git (push)
+```
+
+If you only see one fork referenced:
+
+```sh
+QMKuser ~/qmk_firmware (master)
+$ git remote -v
+origin  https://github.com/qmk/qmk_firmware.git (fetch)
+origin  https://github.com/qmk/qmk_firmware.git (push)
+```
+
+add a new remote with:
+
+```sh
+git remote add upstream https://github.com/qmk/qmk_firmware.git
+```
+
+Then, redirect the `origin` remote to your own fork with:
+
+```sh
+git remote set-url origin https://github.com/<your_username>/qmk_firmware.git
+```
+
+Now that you have both remotes configured, you need to update the references for the upstream repository, which is QMK's, by running:
+
+```sh
+git fetch upstream
+```
+
+At this point, resynchronize your branch to QMK's by running:
+
+```sh
+git reset --hard upstream/master
+```
+
+These steps will update the repository on your computer, but your GitHub fork will still be out of sync. To resynchronize your fork on GitHub, you need to push to your fork, instructing Git to override any remote changes that are not reflected in your local repository. To do this, run:
+
+```sh
+git push --force-with-lease
+```
+
+!> **DO NOT** run `git push --force-with-lease` on a fork to which other users post commits. This will erase their commits.
+
+Now your GitHub fork, your local files, and QMK's repository are all the same. From here you can make further needed changes ([use a branch!](newbs_git_using_your_master_branch.md#making-changes)) and post them as normal.