btrfs: Add treelog mount option.

Add treelog mount option to enable tree log with
remount option.

Signed-off-by: Qu Wenruo <quwenruo@cn.fujitsu.com>
Reviewed-by: David Sterba <dsterba@suse.cz>
Signed-off-by: Josef Bacik <jbacik@fb.com>
Signed-off-by: Chris Mason <clm@fb.com>
diff --git a/Documentation/filesystems/btrfs.txt b/Documentation/filesystems/btrfs.txt
index e05c6ae..d11cc2f 100644
--- a/Documentation/filesystems/btrfs.txt
+++ b/Documentation/filesystems/btrfs.txt
@@ -164,8 +164,9 @@
 	Enable/disable data checksumming for newly created files.
 	Datasum implies datacow.
 
+  treelog(*)
   notreelog
-	Disable the tree logging used for fsync and O_SYNC writes.
+	Enable/disable the tree logging used for fsync and O_SYNC writes.
 
   recovery
 	Enable autorecovery attempts if a bad tree root is found at mount time.