Document derived and define more

[MateuszKubuszok]

TODO:

• product examples
• enum examples
• patchers
• custom transformation section (mention when it is NOT necessary)
• maybe add scaladocs section about using derive/define instead

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 86.92%. Comparing base (0a049ff) to head (d6fd111).

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #693   +/-   ##
=======================================
  Coverage   86.92%   86.92%           
=======================================
  Files         183      183           
  Lines        8185     8185           
  Branches      776      785    +9     
=======================================
  Hits         7115     7115           
  Misses       1070     1070           

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