That's probably the most simple script ever requested Try:
On saving Picard will automatically add the numbers like
(1) at the end, but this can currently not be customized (so you can't set it to e.g. use
 or some other pattern).
Please note that MB / Picard is in general best used on complete albums, that's why you will find most scripts using a structure including the album name. But if you really just care about the song and the artist you can do this of course.