README: Point to git repository
README: Point to git repository

The Mercurial repositories are no more, so update the pointer.

Signed-off-by: Andrea Bolognani <3ada0bee826c753786fdbba72243dfba997094cf@redhat.com>

libvirt/libvirt-cim,libvirt/libvirt-cim,libvirt/libvirt-cim