Update contribution guidelines

[gabegma]

Description:

Add details to the contribution guidelines.

Checklist:

You should check all boxes before the PR is ready. If a box does not apply, check it to acknowledge it.

• [x] ISSUE NUMBER. You linked the issue number (Ex: Resolve #XXX).
• [x] PRE-COMMIT. You ran pre-commit on all commits, or else, you ran pre-commit run --all-files at the end.
• [x] FRONTEND TYPES. Regenerate the front-ent types if you played with types and routes. Run cd webapp && yarn types while the back-end is running.
• [x] USER CHANGES. The changes are added to CHANGELOG.md and the documentation, if they impact our users.
• [x] DEV CHANGES.
  • Update the documentation if this PR changes how to develop/launch on the app.
  • Update the README files and our wiki for any big design decisions, if relevant.
  • Add unit tests, docstrings, typing and comments for complex sections.

[gabegma]

Can you take a look @hughesthe1st ?