Add note about shared models

[bkoelman]

Update documentation about using shared models with auto-generated controllers.

QUALITY CHECKLIST

• Changes implemented in code
• Complies with our contributing guidelines
• Adapted tests
• Documentation updated

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 90.69%. Comparing base (bef0863) to head (c0303b9).
Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1679   +/-   ##
=======================================
  Coverage   90.69%   90.69%           
=======================================
  Files         354      354           
  Lines       11536    11536           
  Branches     1900     1900           
=======================================
  Hits        10462    10462           
  Misses        702      702           
  Partials      372      372           

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