BACK-UPS - If you will have one or more backup musicians, enter name,
email and instrument. If you have more than 3 backups, use Information
for Registrar box.
If you are entering in the Other Instruments or Advanced categories (only),
specify in the Information for Registrar box if one or more of your backups
is to be judged for Best Backup. Backups may only be judged for Best Backup
once for each instrument played.