MAINTAINERS: ksmbd: add entry for documentation

Include Documentation/filesystems/cifs/ksmbd.rst in the ksmbd maintainers
file entry.
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>

MAINTAINERS

@@ -10885,6 +10885,7 @@ R:	Sergey Senozhatsky <senozhatsky@chromium.org>
 L:	linux-cifs@vger.kernel.org
 S:	Maintained
 T:	git git://git.samba.org/ksmbd.git
+F:	Documentation/filesystems/cifs/ksmbd.rst
 F:	fs/ksmbd/
 F:	fs/smbfs_common/