www/gitea: remove barriers for new users (git binary not found in PATH)

[Matthias Petermann <mp%petermann-it.de@localhost>]

Hello,

since I am in the process of switching my repositories from Gitolite to 
Gitea, I have a little suggestion about the pkg of gitolite.

Yesterday I tried to get gitea to work from pkgsrc. It took me quite a 
while to solve a trivial problem. So here briefly the "solution" and a 
suggestion for discussion.

The initial situation is the installation of gitea from pkgsc 2021Q4 via 
pkg_add. After copying the rc-script into /etc/rc.d gitea does not start.

After removing the output redirection > /dev/null from the rc script I 
got an output that gitea cannot find the git binary. Logical: gitea is 
started with the git user whose environment does not include the PATH 
/usr/pkg/bin.

So, since gitea already has the pkg git-base as a dependency, the git 
binary can be assumed to exist under ${PREFIX}/bin. What do you think 
about adding the following to the app.ini.sample?

```
[git]
PATH = @PREFIX@/bin/git
```

This would make gitea usable out of the box for most users.

Kind regards
Matthias