Update instructions on running tests cross platform
Update instructions on running tests cross platform

Fixes #1639

MattGal/wcf,dotnet/wcf,imcarolwang/wcf,mconnew/wcf,mconnew/wcf,imcarolwang/wcf,zhenlan/wcf,StephenBonikowsky/wcf,shmao/wcf,shmao/wcf,zhenlan/wcf,hongdai/wcf,StephenBonikowsky/wcf,ElJerry/wcf,ericstj/wcf,hongdai/wcf,KKhurin/wcf,dotnet/wcf,ElJerry/wcf,imcarolwang/wcf,ericstj/wcf,mconnew/wcf,KKhurin/wcf,dotnet/wcf,MattGal/wcf