docs(nav-controller): full review of docs

[rtpHarry]

Started as a simple typo but ended up reviewing all docs items on the page.

Mostly fixed grammar, and some typos.

One mistake I would like to get an opinion on was that navigateBack was mentioned twice in one docs block. I changed it to navigateRoot but just want to be sure this was the correct change before it ends up in the official docs:

It's recommended to use navigateForward(), navigateBack() and navigateRoot() instead of setDirection().

This is the only change that was "new" content.

Pull request checklist

Please check if your PR fulfills the following requirements:

• Tests for the changes have been added (for bug fixes / features)
• Docs have been reviewed and added / updated if needed (for bug fixes / features)
• Build (npm run build) was run locally and any changes were pushed
• Lint (npm run lint) has passed locally and any fixes were made for failures

Pull request type

Please check the type of change your PR introduces:

• Bugfix
• Feature
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no api changes)
• Build related changes
• Documentation content changes
• Other (please describe):

What is the current behavior?

Issue Number: N/A

What is the new behavior?

Does this introduce a breaking change?

• Yes
• No

Other information

[brandyscarney]

Thank you!