cgroup: add delegation section to unified hierarchy documentation

v2: Rearranged paragraphs as suggested by Johannes Weiner.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
(cherry picked from commit 8a0792ef8e01f03cb43806c6a87738bde34df713)
Signed-off-by: Alex Shi <alex.shi@linaro.org>

Conflicts:
	Documentation/cgroups/unified-hierarchy.txt
1 file changed