contib/mdev.conf: mdevd can rebroadcast uevents natively

contrib/mdev.conf

@@ -1,5 +1,11 @@
 # example rules for mdev.conf
 #
+# NOTE:
+# since https://github.com/skarnet/mdevd/commit/b61ab0373a724d38e059655d561b5fb3dcb2aff6,
+# mdevd can rebroadcast uevents natively which means that you don't need to add anything
+# to /etc/mdev.conf. In order to enable this functionality, you need to add `-O 4` to
+# mdevd arguments.
+#
 # NOTE: replace /path/to/helper with path to compiled binary of helper.c
 
 # handle all uevents(not recommended)