maintainers: Add ISOFS entry

We miss ISOFS entry in MAINTAINERS file. Add it and write me as the
maintainer there since ISOFS is pretty low effort these days. Less
random patches for Andrew to merge ;-).
Signed-off-by: Jan Kara <jack@suse.cz>

MAINTAINERS

@@ -10893,6 +10893,13 @@ F:	drivers/isdn/Makefile
 F:	drivers/isdn/hardware/
 F:	drivers/isdn/mISDN/
 
+ISOFS FILESYSTEM
+M:	Jan Kara <jack@suse.cz>
+L:	linux-fsdevel@vger.kernel.org
+S:	Maintained
+F:	Documentation/filesystems/isofs.rst
+F:	fs/isofs/
+
 IT87 HARDWARE MONITORING DRIVER
 M:	Jean Delvare <jdelvare@suse.com>
 L:	linux-hwmon@vger.kernel.org