I've created a little guide for installing CUPS with AirPrint compatibility on my own blog. I can re-post it here if thats important. This guide reflects the latest FreeNAS changes (mDNSresponder instead of Avahi).
https://www.kaisblog.de/2014/08/27/airprint-jail-freenas/
https://www.kaisblog.de/2014/08/27/airprint-jail-freenas/