fix documentation for IIS reverse proxy configuration

[nexero]

fix #16245 as pull requests won't work properly otherwise

[codecov-commenter]

Codecov Report

Merging #16246 (ae2753c) into main (0393a57) will increase coverage by 1.25%.
The diff coverage is 49.02%.

@@            Coverage Diff             @@
##             main   #16246      +/-   ##
==========================================
+ Coverage   44.24%   45.49%   +1.25%     
==========================================
  Files         695      705      +10     
  Lines       82341    83167     +826     
==========================================
+ Hits        36429    37840    +1411     
+ Misses      40014    39262     -752     
- Partials     5898     6065     +167     

Impacted Files	Coverage Δ
cmd/generate.go	0.00% <0.00%> (ø)
cmd/hook.go	0.00% <0.00%> (ø)
models/action.go	47.12% <ø> (ø)
models/oauth2.go	28.00% <0.00%> (-1.17%)	⬇️
models/repo_archiver.go	0.00% <0.00%> (ø)
models/user.go	52.32% <ø> (-1.07%)	⬇️
modules/context/repo.go	52.99% <0.00%> (-0.30%)	⬇️
modules/generate/generate.go	0.00% <0.00%> (-16.00%)	⬇️
modules/git/error.go	50.00% <0.00%> (-4.24%)	⬇️
modules/git/last_commit_cache_nogogit.go	35.84% <0.00%> (+0.66%)	⬆️
... and 189 more

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[zeripath]

Ok so looking at the docs here it appears by default that the following characters are disallowed:

<,>,*,%,&,:,\

I guess we really only need the : but gitea is safe with all of these characters.