Auto revert mode but only for git projects

[Andrea Crotti <andrea.crotti.0@gmail.com>]

When using branches with emacs reverting the buffers can be quite
tedious.

But also activating auto-revert-mode everywhere is not such a good idea.

So I thought that I could automatically activate auto-revert-mode BUT
only when
1. I'm in a git repo
2. I have at least 2 branches

What could be the cleaner way to do it?
Textmate.el has already something to look if it's a git repo, then I can
check for more branches with
--8<---------------cut here---------------start------------->8---
git branch | wc -l
--8<---------------cut here---------------end--------------->8---
for example and maybe add a hook in find-file-hooks?

Could that work?