Update GitHub documentation

[samglover]

This is a PR for updates related to the LIT Lab's 2024 summer cohort. In the course of that work it became clear we needed to update the GitHub instructions to help student teams work together. This update primarily addresses that, along with some additional minor changes.

Some notes:

• I removed a whole lot of stuff from the GitHub page and reorganized it around workflow, how-tos, best practices, and troubleshooting. I know how it can feel to get edited this extensively, and I hope @plocket, who wrote most or all of the existing page, will forgive me.
• A lot of what I removed (as opposed to reorganized and revised) was (1) duplicative of GitHub or Docassemble documentation, so I replaced it with links, and (2) related to managing files, packages, and projects in the Docassemble playground but not necessarily related to GitHub (and a lot of this can also be found in the Docassemble docs).
• I resolved the broken links and anchors related to my changes. I did not resolve broken anchors related to the ALKiln pages since as far as I know they are still a work in progress.
• I will continue working on this branch after this PR is merged. There's lots more to do but I felt this was worth pushing out now.

[samglover]

@nonprofittechy I made a few updates in order to include information about uploading a package, and that led me to add some further notes on naming packages before publishing to GitHub (addressing #434). Which then made me realize the name formats page was not showing up anywhere in the sidebar, so I fixed that, too.