Documentation: cgroup: add documentation for net_cls cgroups.

This patch adds a new file, Documentation/cgroups/net_cls.txt, with info
about net_cls cgroups, and updates the 00-INDEX accordingly.

Signed-off-by: Rami Rosen <ramirose@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/Documentation/cgroups/00-INDEX b/Documentation/cgroups/00-INDEX
index f5635a0..bc461b6 100644
--- a/Documentation/cgroups/00-INDEX
+++ b/Documentation/cgroups/00-INDEX
@@ -18,6 +18,8 @@
 	- Memory Resource Controller; implementation details.
 memory.txt
 	- Memory Resource Controller; design, accounting, interface, testing.
+net_cls.txt
+	- Network classifier cgroups details and usages.
 net_prio.txt
 	- Network priority cgroups details and usages.
 resource_counter.txt