add contrib section to README
add contrib section to README

Strauman/Viewpoint,makandra/Viewpoint,Tsoondev/Viewpoint,Windermere/Viewpoint,Gerd82/Viewpoint,Datacom/Viewpoint,getoutreach/Viewpoint,WinRb/Viewpoint,gshutler/Viewpoint,bcherrington/Viewpoint,albertdang/Viewpoint