Docs: add experimental warning to CDB to PyMechanical example

[greschd]

Add the warning that PyMechanical integration is experimental to the CDB to PyMechanical example, since it uses the helper function to load the ACPCompositeDefinitions.h5 into Mechanical.

Closes #735

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 94.99%. Comparing base (6017106) to head (db7f030).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #736   +/-   ##
=======================================
  Coverage   94.99%   94.99%           
=======================================
  Files         109      109           
  Lines        5695     5695           
  Branches      322      322           
=======================================
  Hits         5410     5410           
  Misses        284      284           
  Partials        1        1           

Flag	Coverage Δ
direct-launch	91.58% <ø> (ø)
minimum-deps	93.19% <ø> (ø)
python-3.10	94.25% <ø> (ø)
python-3.11	94.18% <ø> (ø)
python-3.12	94.38% <ø> (ø)
server-2024R2	90.81% <ø> (ø)
server-2025R1	94.18% <ø> (ø)
server-2025R2	94.18% <ø> (ø)
server-latest	94.80% <ø> (ø)

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