Add missing files from panda-dist.tar.gz

There are files missing from panda-dist.tar.gz at http://panda.trailing-edge.com/, which I think would be good to add to this repo for completeness. Examples are `CPYRIGHT`, `README`, `README-MULTIUNIT-RP07`; perhaps also `RH20.RP07.1`. (No need to include the klh10-2.0h and executables based on that, of course.)