MAINTAINERS: add Vladimir as co-maintainer of NBD

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Message-Id: <20210304103503.21008-1-vsementsov@virtuozzo.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Eric Blake <eblake@redhat.com>

MAINTAINERS

@@ -3033,6 +3033,7 @@ F: block/iscsi-opts.c
 
 Network Block Device (NBD)
 M: Eric Blake <eblake@redhat.com>
+M: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
 L: qemu-block@nongnu.org
 S: Maintained
 F: block/nbd*
@@ -3043,6 +3044,7 @@ F: blockdev-nbd.c
 F: docs/interop/nbd.txt
 F: docs/interop/qemu-nbd.rst
 T: git https://repo.or.cz/qemu/ericb.git nbd
+T: git https://src.openvz.org/scm/~vsementsov/qemu.git nbd
 
 NFS
 M: Peter Lieven <pl@kamp.de>