Add documentation for the Outline pane

[hyounes4560]

Pull Request

Pull Request Checklist

• [x] Read and followed this repo's Contributing Guidelines
• [x] Based your PR on the latest version of the correct branch (master or 4.x)
• [x] Checked your writing carefully for correct English spelling, grammar, etc
• [x] Described your changes and the motivation for them below
• [x] Noted what issue(s) this pull request resolves, creating one if needed

Description of Changes

Add a new section for the Outline pane as per @CAM-Gerlach suggestion.

Issue(s) Resolved

Fixes #326

[CAM-Gerlach]

Thanks @hyounes4560 for all your hard work on this! I apologize for my absence over the past week; my mom's living situation became unstable again and I had to go help her move (again).

Per your request, I went ahead and took care of the minor changes as commits on my side. The changes are:

• Tweaking the crop on the options menu image to omit the area below, which was taking up a good deal of vertical space, and compressing the resulting image
• Cleaning up line breaks and spaces
• Fixing a couple issues with the reST formatting (particularly GDocs' mangling of the :menuselection: syntax) and applying reST formatting a few other places
• Using consistent capitalization (Outline to refer to the pane and outline to the actual outline construct) and verb tense in the Options menu list

I broke them up into separate commits for your review, but they'll all be squashed into your commit when this is merged. Thanks!

[jitseniesen]

Looks good; well done, Hanan! No further comments from me.

[CAM-Gerlach]

Pro tip—I find it a good habit to always git pull before I make any local changes to pick up any remote ones you or others pushed the the PR, as it avoids the merge conflict and related issues you ran into here (as otherwise, if I don't make it a habit, I find it easy to forget).

Also, quick reminder, you can apply multiple suggestions at time with the same message by (on the Filestab) clicking Add to batch on each suggestion and then Commit once you'd added all of them.

So long as we're squash merging, neither of these issues poses major problems at our end—but it can certainly help things go smoother on yours :)