Describe how to get extra packages from OPM repo

I actually done expect this to get committed (yet), since it contains reference to the mythological URL http://opm-project.org/packages/redhat, but at least it kicks off the discussion about where to host the APEL (Arne Morten's Packages for Enterprise Linux ;-)) packages.

(If anyone has virtual machines in abundance, they can use the URL http://folk.uib.no/rka081/pkgs/rpm instead, where I have put up a snapshot I got earlier (before it was complete, you must --disable-ert))