There isn't an official guide on the website, some staff might know how, I'm not sure.
This is the Client support section of BolehVPN:
https://www.bolehvpn.net/clients-installations/Pfsense isn't something typically supported through a VPN service, and usually when someone is stepping up to this level, it's considered they're experienced to do it on their own.
I have used Pfsense in the past, I found it pretty straight forward, install the OpenVPN package, then go through the settings of Pfsense based off the options you see listed in the .ovpn config files.
All I can tell you is there is a lot of information online that can help guide you in the right direction to get a good feel for this. If this doesn't work for you, Pfsense has an IRC channel on Freenode, where you can get real time support.