I'd be happy to take review comments and changes to apply.
The service runs, but due to limitations of our guix system vm
(https://lists.gnu.org/archive/html/guix-devel/2016-08/msg01816.html)
I was not able to test a situation where I add a pubkey to $HOME/.ssh/
of user "git", export a repository, clone it from VM to HOST and push
some changes to the git daemon running on the VM.
I know I should add a section about it to documentation, but first I
want to get comments for the service as it currently is.