docs/cgroup: add entry for misc.events

Added descriptions of misc.events.
Signed-off-by: Chunguang Xu <brookxu@tencent.com>
Reviewed-by: Michal Koutný <mkoutny@suse.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

Documentation/admin-guide/cgroup-v2.rst

@@ -2310,6 +2310,16 @@ Miscellaneous controller provides 3 interface files. If two misc resources (res_
         Limits can be set higher than the capacity value in the misc.capacity
         file.
 
+  misc.events
+	A read-only flat-keyed file which exists on non-root cgroups. The
+	following entries are defined. Unless specified otherwise, a value
+	change in this file generates a file modified event. All fields in
+	this file are hierarchical.
+
+	  max
+		The number of times the cgroup's resource usage was
+		about to go over the max boundary.
+
 Migration and Ownership
 ~~~~~~~~~~~~~~~~~~~~~~~