Github ovirt PRs automatic response

Hi,

The majority of the oVirt projects are developped in gerrit while github
repository are just a mirror.

Sometimes, contributors are sending PR to the github.
We should have an automatic response to their PR with an explanantion and a
link to the gerrit page in ovirt.org.

Of course, it should be enable only on the projects that are hosted in
gerrit.

Regards,

Fred Rolland