docs: explain how to find a clang-format patch generated by CI

[intelliot]

Fix #4020

[oeggert]

I'll review it today.

[ximinez]

I think it would also be useful to have these instructions in the "What happened?" step of the clang-format.yml job.

[intelliot]

@ximinez is this PR worth merging as-is? If not, let's close it, and you can open a new PR with your preferred changes.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 71.3%. Comparing base (9f7c619) to head (4e41a3d).

Additional details and impacted files

@@            Coverage Diff            @@
##           develop   #4521     +/-   ##
=========================================
- Coverage     71.3%   71.3%   -0.0%     
=========================================
  Files          796     796             
  Lines        66966   66966             
  Branches     10866   10870      +4     
=========================================
- Hits         47770   47762      -8     
- Misses       19196   19204      +8     

see 2 files with indirect coverage changes