refs #100647 Update README.darwin details on how to build a universal binary target.
refs #100647 Update README.darwin details on how to build a universal
binary target.

svartika/ccnx,cawka/ndnx,cawka/ndnx,svartika/ccnx,cawka/ndnx,svartika/ccnx,svartika/ccnx,cawka/ndnx,svartika/ccnx,svartika/ccnx,cawka/ndnx,svartika/ccnx