Staging: autofs3: create TODO file

This lists what's going to happen to the filesystem (i.e. removal
in 2.6.38 unless someone steps up to maintain it.)

Cc: Arnd Bergmann <arnd@arndb.de>
Cc: H. Peter Anvin <hpa@zytor.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>