ext4: import journal chapter from wiki page

Import the chapter about the journal from the on-disk format wiki
page into the kernel documentation.
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

Documentation/filesystems/ext4/ondisk/globals.rst

@@ -10,3 +10,4 @@ have static metadata at fixed locations.
 .. include:: group_descr.rst
 .. include:: bitmaps.rst
 .. include:: mmp.rst
+.. include:: journal.rst