JFS: document uid, gid, and umask mount options in jfs.txt

Signed-off-by: Dave Kleikamp <shaggy@austin.ibm.com>

Documentation/filesystems/jfs.txt

@@ -29,7 +29,13 @@ errors=continue		Keep going on a filesystem error.
 errors=remount-ro	Default. Remount the filesystem read-only on an error.
 errors=panic		Panic and halt the machine if an error occurs.
 
-Please send bugs, comments, cards and letters to shaggy@austin.ibm.com.
+uid=value	Override on-disk uid with specified value
+gid=value	Override on-disk gid with specified value
+umask=value	Override on-disk umask with specified octal value.  For
+		directories, the execute bit will be set if the corresponding
+		read bit is set.
+
+Please send bugs, comments, cards and letters to shaggy@linux.vnet.ibm.com.
 
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