docs: cgroup-v1: add it to the admin-guide book

Those files belong to the admin guide, so add them.

Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
diff --git a/security/device_cgroup.c b/security/device_cgroup.c
index c071965..725674f 100644
--- a/security/device_cgroup.c
+++ b/security/device_cgroup.c
@@ -509,7 +509,7 @@ static inline int may_allow_all(struct dev_cgroup *parent)
  * This is one of the three key functions for hierarchy implementation.
  * This function is responsible for re-evaluating all the cgroup's active
  * exceptions due to a parent's exception change.
- * Refer to Documentation/cgroup-v1/devices.rst for more details.
+ * Refer to Documentation/admin-guide/cgroup-v1/devices.rst for more details.
  */
 static void revalidate_active_exceptions(struct dev_cgroup *devcg)
 {