Document release process

[dweindl]

Closes #2942.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 77.49%. Comparing base (35c3492) to head (ca47e2e).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3059      +/-   ##
==========================================
- Coverage   78.15%   77.49%   -0.66%     
==========================================
  Files         311      311              
  Lines       20641    20641              
  Branches     1499     1499              
==========================================
- Hits        16131    15995     -136     
- Misses       4500     4636     +136     
  Partials       10       10              

Flag	Coverage Δ
cpp	70.77% <ø> (-0.02%)	⬇️
cpp_python	37.23% <ø> (ø)
petab	45.86% <ø> (ø)
petab_sciml	13.77% <ø> (ø)
python	69.43% <ø> (-0.01%)	⬇️
sbmlsuite-jax	?

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see 8 files with indirect coverage changes

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