MAINTAINERS: add new cgroup list to CC notice

As discussed at Kernel Summit(2011), new cgroups mailing list is opened
by James.  This list is for discussing general cgroup design and patches
including all subsystems and for getting more attentions to
cgroups/namespaces related issues by developpers.

Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: James Bottomley <James.Bottomley@HansenPartnership.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>