Update regression docs

[lintool]

Update docs to make sure we have good record-keeping.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 66.02%. Comparing base (f5c6929) to head (8fa5000).
Report is 2 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff            @@
##             master    #2671   +/-   ##
=========================================
  Coverage     66.02%   66.02%           
  Complexity     1488     1488           
=========================================
  Files           225      225           
  Lines         13023    13023           
  Branches       1553     1553           
=========================================
  Hits           8598     8598           
  Misses         3894     3894           
  Partials        531      531           

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