doc: Update README with new build instructions

Change-Id: If81fd28cfe62fc1f59129b009d2d687625e102b6
Signed-off-by: Adam Litke <alitke@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/23870
Reviewed-by: Sandro Bonazzola <sbonazzo@redhat.com>
Reviewed-by: Kiril Nesenko <knesenko@redhat.com>