[Draft] Add docs contribution checklist page

[tetrapod00]

Resolves #9193.

This PR adds a new page to the Writing documentation section. It is a list of all of the content, style, and formatting guidelines that manual contributions are expected to follow. Each entry in the page concisely summarizes the guideline, then links to the section of docs that describes the guideline in full.

It is intended to be used:

• By contributors to check their own work, in order to (hopefully) reduce the work needed during reviews.
• By reviewers to see a summary of guidelines while reviewing. The links should make it easier to cite guidelines and link to rules when reviewing.

#10169 needs to be merged first, since this references some guidelines in that PR.