docs: Document how to use primary keys

[AndreasAlbertQC]

Motivation

We are currently lacking verbose documentation of some of our features.

Closes #153

Changes

• Restructured documentation to add a new features folder for verbose documentation on specific features users might be looking for.
• Added a documentation page for primary keys.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (5d1c4d7) to head (51a6c39).
⚠️ Report is 4 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##              main      #157   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           51        51           
  Lines         2896      2896           
=========================================
  Hits          2896      2896           

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[borchero]

Thank you! :)