Add documentation on how to do good OSS documentation

## Feature

We would like to have better documentation on how to create good open source software documentation as guidance for Department organizations wishing to open source things. This should include things like relevant sections of a "contributing" doc (not just a link to an example), how to write and review PRs, good commit messages, how to write a good GH issue, etc.

## Page(s) Affected

This could go on https://www.code.mil/how-to-open-source.html ("How to Open Source"), but it could live on it's own page, linked a couple of places.

Start by reading the existing https://www.code.mil/how-to-open-source.html page and review the requested guidance areas in this issue: contributing documents, pull requests, commit messages, and GitHub issues. Done means the guidance is written, placed on that page or a linked new page, and linked from the relevant locations.

Do mô hình lập chỉ mục viết ra từ nội dung của issue.