doc: Add caveats section

[dweindl]

Make users aware of some known potential issues (e.g., #18, #2707, #2724, #2673).

And update .gitignore.

👀 https://amici--2735.org.readthedocs.build/en/2735/python_caveats.html

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 77.94%. Comparing base (666a450) to head (1ae25b9).
Report is 2 commits behind head on develop.

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #2735   +/-   ##
========================================
  Coverage    77.94%   77.94%           
========================================
  Files          327      327           
  Lines        23065    23065           
  Branches      1484     1484           
========================================
  Hits         17977    17977           
  Misses        5077     5077           
  Partials        11       11           

Flag	Coverage Δ
cpp	74.80% <ø> (ø)
cpp_python	33.62% <ø> (ø)
petab	39.35% <ø> (ø)
python	72.97% <ø> (ø)

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