Changes

github: enable lockdown of issues and merge requests
Libvirt uses GitHub as an automated read-only mirror. The goals were to 
have a disaster recovery backup for libvirt.org, a way to make it easy 
for people to clone their own private copy of libvirt Git, and finally 
as a way to interact with apps like Travis.
The project description was set to a message telling people that we 
don't respond to pull requests. This was quite a negative message to 
potential contributors, and also did not give them any guidance about 
the right way to submit to libvirt. Many also missed the description and 
submitted issues or pull requests regardless.
It is possible to disable the issue tracker in GitHub, but there is no 
way to disable merge requests. Disabling the issue tracker would also 
leave the problem of users not being given any positive information 
about where they should be reporting instead.
There is a fairly new 3rd party application built for GitHub that 
provides a bot which auto-responds to both issues and merge requests, 
closing and locking them, with a arbitrary comment:
   https://github.com/apps/repo-lockdown
This commit adds a suitable configuration file for libvirt, which tries
to give a positive response to user's issue/pullreq and guide them to
the desired contribution path on GitLab.
Reviewed-by: Andrea Bolognani <abologna@redhat.com> Reviewed-by: Pavel
Hrdina <phrdina@redhat.com> Reviewed-by: Eric Blake <eblake@redhat.com> 
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>