Subject: contributing: Broken link to Git manual

From: Maxime Devos <[email-masked]>
Date: Mon, 06 Jun 2022 20:22:20 +0200

contributing.texi contains:

@pxref{submitting patches,, Submitting patches to a project, git, Git User Manual}).

However, there is no 'git' info manual.  I guess the ', git,' should
be replaced by ',,' or something like that to avoid implying there's
a git info page?

Greetings,
Maxime.