bug#55821: contributing: Broken link to Git manual

[Maxim Cournoyer]

Hi Ludo,

Ludovic Courtès <ludo@gnu.org> writes:

> Maxime Devos <maximedevos@telenet.be> skribis:
>
>> contributing.texi contains:
>>
>> @pxref{submitting patches,, Submitting patches to a project, git, Git User 
>> Manual}).
>>
>> However, there is no 'git' info manual.
>
> I think there used to be one; could it be that we’re no longer building
> it?

Indeed, support for it was contributed by David Kastrup in 2007 [0].  It
seems we should be running 'make install-info' explicitly.  Perl is
needed, unless that bit changed.

[0]  https://github.com/git/git/commit/4739809cd0ea12a8de006f9f086fdff9285189b8

Thanks,

Maxim