CONTRIBUTING.md: add bullet point about the merge process (#1416)

Signed-off-by: Achille Roussel <[email protected]>
Co-authored-by: Crypt Keeper <[email protected]>

CONTRIBUTING.md

@@ -57,8 +57,19 @@ You can add the sign off when creating the git commit via `git commit -s`.
 
 ## Code Reviews
 
-* A single approval is sufficient to merge. If a reviewer asks for changes in a PR they should be
-addressed before the PR is merged, even if another reviewer has already approved the PR.
-* During the review, address the comments and commit the changes _without_ squashing the commits.
-This facilitates incremental reviews since the reviewer does not go through all the code again to
-find out what has changed since the last review.
+* The pull request title should describe what the change does and not embed issue numbers.
+The pull request should only be blank when the change is minor. Any feature should include
+a description of the change and what motivated it. If the change or design changes through
+review, please keep the title and description updated accordingly.
+* A single approval is sufficient to merge. If a reviewer asks for
+changes in a PR they should be addressed before the PR is merged,
+even if another reviewer has already approved the PR.
+* During the review, address the comments and commit the changes
+_without_ squashing the commits. This facilitates incremental reviews
+since the reviewer does not go through all the code again to find out
+what has changed since the last review. When a change goes out of sync with main,
+please rebase and force push, keeping the original commits where practical.
+* Commits are squashed prior to merging a pull request, using the title
+as commit message by default. Maintainers may request contributors to
+edit the pull request tite to ensure that it remains descriptive as a
+commit message. Alternatively, maintainers may change the commit message directly.