cpusets: document proc status cpus and mems allowed lists

Provide a little documentation for the two new fields, Cpus_allowed_list
and Mems_allowed_list, that were added to each /proc/<pid>/status file a
while back.

Signed-off-by: Paul Jackson <pj@sgi.com>
Acked-by: Michael Kerrisk <mtk.manpages@gmail.com>
Cc: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>