docs: filesystems: Reduce ext2.rst to one top-level heading

This prevents the other headings like "Options" and "Specification" from
leaking out and being listed separately in the table of contents.

Link: https://lore.kernel.org/r/20201108004045.1378676-1-j.neuschaefer@gmx.net
Signed-off-by: Jonathan Neuschäfer <j.neuschaefer@gmx.net>
Signed-off-by: Jan Kara <jack@suse.cz>
diff --git a/Documentation/filesystems/ext2.rst b/Documentation/filesystems/ext2.rst
index d83dbbb..c2fce22 100644
--- a/Documentation/filesystems/ext2.rst
+++ b/Documentation/filesystems/ext2.rst
@@ -1,6 +1,7 @@
 .. SPDX-License-Identifier: GPL-2.0
 
 
+==============================
 The Second Extended Filesystem
 ==============================