add documentation for the call site feature

[MBurchard]

fixes #41

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (c8e872b) to head (0e6878f).
Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##              main       #42   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            8         8           
  Lines          795       795           
  Branches       289       289           
=========================================
  Hits           795       795           

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