aufs doc: LSM may be a good additional info

Signed-off-by: J. R. Okajima <hooanon05g@gmail.com>
(cherry picked from commit 7555811a8741218089016a6abed15a440baca476)

Documentation/filesystems/aufs/README

@@ -323,6 +323,7 @@ know with:
   system, instead of the date you downloaded.
 - configuration (define/undefine CONFIG_AUFS_xxx)
 - kernel configuration or /proc/config.gz (if you have it)
+- LSM (linux security module, if you are using)
 - behaviour which you think to be incorrect
 - actual operation, reproducible one is better
 - mailto: aufs-users at lists.sourceforge.net