To use customers the organization package has to be installed. Then PM can try to figure out where to use it. Once it has found it, a link appears to add a customer. And no, to my knowledge there does not exist a public documentation yet, but I would be totally surprised if Jade/Alex did not write one for their company (and we need to write one in German soon, though for the HEAD version, which differs, and only for the parts we need).
