Update of Documentation/cgroups/00-INDEX

unified-hierarchy.txt was added by 6573157 (cgroup: add documentation
about unified hierarchy)

Cc: Tejun Heo <tj@kernel.org>
Cc: Li Zefan <lizefan@huawei.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: cgroups@vger.kernel.org
Cc: linux-doc@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Henrik Austad <henrik@austad.us>
Signed-off-by: Tejun Heo <tj@kernel.org>

Documentation/cgroups/00-INDEX

@@ -24,3 +24,5 @@ net_prio.txt
 	- Network priority cgroups details and usages.
 resource_counter.txt
 	- Resource Counter API.
+unified-hierarchy.txt
+	- Description the new/next cgroup interface.