docs: append coding guidelines to maintainer docs

[phm07]

This PR adds coding guidelines to our docs.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 79.42%. Comparing base (6afa559) to head (b34feff).
⚠️ Report is 9 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #790      +/-   ##
==========================================
- Coverage   80.05%   79.42%   -0.64%     
==========================================
  Files          60       60              
  Lines        4452     4553     +101     
==========================================
+ Hits         3564     3616      +52     
- Misses        587      634      +47     
- Partials      301      303       +2     

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[jooola]

Do not hesitate to also use actual code with a lot of comments to describe patterns.

[phm07]

Is there maybe something else that we could add to the guidelines?

[jooola]

Is there maybe something else that we could add to the guidelines?

A bunch of points in our internal document are still missing from this documentation. Those could be included as well.