Same problem previously reported. It still happens. Went to follow link for more info about the backup/restore and while the URL reads http://www.zenphoto.org/documentation/plugins/_plugins---backup_restore.php.html/ it's taken me to the page called Testimonials.
Sorry, but the backup/restore script is new and no documentation run has been yet made that includes it. You will have to make do with reading the script itself.
Generally speaking, you should not expect new features that show up in the development stream to be fully documented the moment they show up.