feat(docs): create Writing Style Guide

[hbar1st]

Checklist:

• I have read freeCodeCamp's contribution guidelines.
• My pull request has a descriptive title (not a vague title like Update index.md)

After reviewing along-side @majestic-owl448 the following PRs
freeCodeCamp/freeCodeCamp#65926
freeCodeCamp/freeCodeCamp#65511
freeCodeCamp/freeCodeCamp#65730

I thought it might be a good idea for fCC to have a writing style guide that would help clarify the use of punctuation in various circumstances. Discussed this with Ilenia, who suggested that I go ahead and open this PR to allow the fCC editors to have a starting point to work from in order to provide that needed clarity in future.

Note

I based some of these rules on the writing style guide used by the US government
Microsoft and the Chicago Manual of Style
The ellipsis formatting comes from the GPO style guide as the MS guide doesn't utilitize en spacing between the dots.
I leave it to the reviewers to pick between them. They both however use a single space before the ellipses (it is treated as a word essentially unlike the current method that fCC utilizes which doesn't have that leading space when the ellipse is at the end of the line)

[majestic-owl448]

additional style rule: front-end, back-end and full-stack needs to be written like this with the dash, i.e., not full stack, or frontend. See freeCodeCamp/freeCodeCamp#62247 (comment)

(may be updated, discussion is in progress) confirmed per freeCodeCamp/freeCodeCamp#65976 (comment)

[hbar1st]

front-end, back-end and full-stack needs to be written like this with the dash

I think the rule should be more general? So use a hyphen in between compounded words that form a single meaning. (eg front and end together form a new concept front-end)

[majestic-owl448]

you find all three forms all over the web, fullstack, full stack and full-stack, so I think it is a good idea to be clear on which form we use. In this case a specific rule I think fits

[hbar1st]

In this case a specific rule I think fits

I added an 8th rule. Hopefully it satisfies the request.