Add MyST-Parser and link community files in docs sidebar

[julianz-]

Add myst-parser to docs dependencies and Sphinx extensions, enabling Markdown support. Link the Code of Conduct and License in the docs sidebar as an initial test of the integration.

❓ What kind of change does this PR introduce?

• 🐞 bug fix
• 🐣 feature
• 📋 docs update
• 📋 tests/coverage improvement
• 📋 refactoring
• 💥 other

📋 What is the related issue number (starting with #)

Resolves #

❓ What is the current behavior? (You can also link to an open issue here)

❓ What is the new behavior (if this is a feature change)?

📋 Other information:

📋 Contribution checklist:

(If you're a first-timer, check out
[this guide on making great pull requests][making a lovely PR])

• I wrote descriptive pull request text above
• I think the code is well written
• I wrote [good commit messages]
• I have [squashed related commits together][related squash] after
  the changes have been approved
• Unit tests for the changes exist
• Integration tests for the changes exist (if applicable)
• I used the same coding conventions as the rest of the project
• The new code doesn't generate linter offenses
• Documentation reflects the changes
• The PR relates to only one subject with a clear title
  and description in grammatically correct, complete sentences

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 77.77%. Comparing base (3937fe1) to head (4d6933a).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #835      +/-   ##
==========================================
- Coverage   78.19%   77.77%   -0.42%     
==========================================
  Files          41       41              
  Lines        4788     4788              
  Branches      547      547              
==========================================
- Hits         3744     3724      -20     
- Misses        905      922      +17     
- Partials      139      142       +3