docs: Improve displaying GitHub API links on pkg.go.dev

[alexandear]

Before:

https://pkg.go.dev/github.com/google/go-github/v79/github#MarketplaceService.GetPlanAccountForAccount

After:

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.43%. Comparing base (3afe183) to head (18cdf89).
⚠️ Report is 2 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #3845   +/-   ##
=======================================
  Coverage   92.42%   92.43%           
=======================================
  Files         197      198    +1     
  Lines       14167    14175    +8     
=======================================
+ Hits        13094    13102    +8     
  Misses        884      884           
  Partials      189      189           

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[alexandear]

I also need to update the generator.

[alexandear]

@gmlewis updated the generator and added a test. Ready for review.

[gmlewis]

Thank you, @alexandear!
LGTM.
Merging.