update nginx config file hint

Created by: darkrasid

I recreate this PR because previous one takes wrong branches.

9882

When use gitlab with relative url, user should change location regular expression on nginx config file.

Because example of nginx config file contain this type regular expression.

^/[\w\.-]+/[\w\.-]+/(info/refs|git-upload-pack|git-receive-pack)$

it will catch some URL like below.

/project/repo.git/git-upload-pack

However if user set relative url, upper url should be

/relative_url/project/repo.git/git-upload-pack

so regular expression isn't able to catch.

It makes errors when cloing, pulling, pushing or archiving.
(ex. it will clone empty repository, even if the repository does not empty.)

I think it is better way that comment to user in example of nginx config file