Docs: clean up key-spacing docs (fixes #9900)

[abiduzz420]

What is the purpose of this pull request? (put an "X" next to item)

[x] Documentation update
[ ] Bug fix (template)
[ ] New rule (template)
[ ] Changes an existing rule (template)
[ ] Add autofixing to a rule
[ ] Add a CLI option
[ ] Add something to the core
[ ] Other, please explain:

What changes did you make? (Give an overview)
Categorized key-spacing options based on their values.

Is there anything you'd like reviewers to focus on?
No

[platinumazure]

Hi @abiduzz420, thanks for the PR!

Just a quick summary of what the failed status checks mean:

• AppVeyor/Travis: Our Markdown linting prefers that we use 4 spaces for indenting sub-lists; I see 2 spaces in this PR. There may be other issues, so please take a look at the "Details" links for those two status checks to see if there's anything else.
• commit-message: The commit message should start with a tag, like "Docs:". Also, we prefer that the message ends with "(fixes Clean up key-spacing documentation #9900)", just so the commit messages look uniform in our changelog.

Once you have 2 or more commits in a pull request, we check the PR title in the commit-message check. So my suggestion would be to push a 2nd commit to fix the Markdown lint issues, and then change the PR title to fix the commit-message check.

Thanks for your understanding!

[platinumazure]

LGTM, thanks! I'd like to wait for one more review before merging.

[not-an-aardvark]

Thanks for contributing!