docs: Fix a broken relref link

[sapk]

A little PR to fix a broken link on current doc : https://docs.gitea.io/en-us/hacking-on-gitea/#creating-new-configuration-options

I based myself on a link that work on the same page : https://github.com/go-gitea/gitea/blame/master/docs/content/doc/advanced/hacking-on-gitea.en-us.md#L94

[codecov-io]

Codecov Report

Merging #7233 into master will increase coverage by <.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #7233      +/-   ##
==========================================
+ Coverage   40.96%   40.97%   +<.01%     
==========================================
  Files         462      462              
  Lines       62567    62567              
==========================================
+ Hits        25630    25635       +5     
+ Misses      33575    33571       -4     
+ Partials     3362     3361       -1

Impacted Files	Coverage Δ
models/repo_list.go	73.09% <0%> (+1.01%)	⬆️
modules/process/manager.go	81.15% <0%> (+4.34%)	⬆️

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