docs: generate table of contents

[phm07]

This PR adds mkdoc to generate a table of contents for long doc files.
We might consider adding this for other doc files as well. Also we probably want to run this as an automated task, for example as a pre-commit hook or a mise task.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 67.48%. Comparing base (eeb8f68) to head (9d1295c).
⚠️ Report is 3 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1305      +/-   ##
==========================================
- Coverage   72.50%   67.48%   -5.03%     
==========================================
  Files         302      302              
  Lines       10995    10995              
==========================================
- Hits         7972     7420     -552     
- Misses       2150     2652     +502     
- Partials      873      923      +50     

Flag	Coverage Δ
e2e	?
unit	67.48% <ø> (ø)

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