Documentation: update cgroups notes
Documentation: update cgroups notes

- ns cgroup has been removed.
- it's true moving a task to another cgroup can fail.

Signed-off-by: Li Zefan <5dc16b054e85ffba6c8d314d8e55ae95dcab12a5@cn.fujitsu.com>
Acked-by: Paul Menage <a027184a55211cd23e3f3094f1fdc728df5e0500@paulmenage.org>
Signed-off-by: Randy Dunlap <6f29df8e90a57f1ba61ffd63b0468c86bb6d3a99@xenotime.net>
Signed-off-by: Linus Torvalds <69652caca27c8b940640ad396ab71f93cacec34f@linux-foundation.org>

KristFoundation/Programs,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas