[docs] Improve contributing docs

[fyliu]

Overview

We need better contributing docs so that contributors know what to do and what to expect

Action Items

• Move most or all sections out of contributing page and create links to them from the page
• Keep the contributing page short but usable by experienced devs
• Link to detailed pages for clarification and for inexperienced devs
• Make sure the clarifications below are part of the docs

Resources/Instructions

• Things that need clarification
  • The supported workflow
    • fork, create feature branch, work, commit, push to fork, create PR from fork to hackforla/peopledepot/main
  • priority goals for the repo:
    • keep as much history as possible
      • prefer rebase merge over squash merge
    • keep the main branch linear for ease of debug
      • merge commits are hard to follow because commits are in another branch
    • keep the commit history clean
      • avoid fix commits if the original commit is in the same PR. Just redo the original commit to include the fix
        • use fixup messages and rebase to modify the original commits
      • changes should be divided into logical commits
  • Every commit in hackforla/peopledepot/main should be runnable.
    • No WIP commits or nonsense commits
  • The way to test GHA is also to test it in a fork
    • For tests against the project board, get a copy of the board from another team member
  • To keep the hackforla/peopledepot/main branch linear, the acceptable PR merging methods are rebase and squash. This means:
    • It's okay to do merge commits in feature branches, provided that you're okay with having them squashed during the final merge
    • The preferred way is to always do rebase to pull in new code. The individual commits in the feature branch can then be rebased during the final merge, provided they're cleaned up (each commit runs, no fixup commits).