Joining registry maintainers

Docker-DCO-1.1-Signed-off-by: Olivier Gambier <olivier@docker.com> (github: dmp42)

registry/MAINTAINERS

@@ -2,3 +2,4 @@ Sam Alba <sam@dotcloud.com> (@samalba)
 Joffrey Fuhrer <joffrey@dotcloud.com> (@shin-)
 Ken Cochrane <ken@dotcloud.com> (@kencochrane)
 Vincent Batts <vbatts@redhat.com> (@vbatts)
+Olivier Gambier <olivier@docker.com> (@dmp42)