docs: Extend the description of ref parameters

[alexandear]

ref descriptions are copied from the appropriate pages in GitHub documentation.

Updates #3630

[gmlewis]

Thank you, @alexandear!
LGTM.
Merging.

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 5 lines in your changes missing coverage. Please review.

Project coverage is 91.32%. Comparing base (74b2ca0) to head (9209c58).
Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
example/commitpr/main.go	0.00%	5 Missing ⚠️

Additional details and impacted files

@@ Coverage Diff @@## master #3643 +/- ##
==========================================
- Coverage 91.33% 91.32% -0.02% 
==========================================
Files 184 184 Lines 16174 16176 +2 ==========================================
Hits 14773 14773 - Misses 1227 1229 +2 
Partials 174 174 

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