Update prerequisites to run docfx (#1631)
Update prerequisites to run docfx (#1631)

#1628
pascalberger/docfx,928PJY/docfx,928PJY/docfx,DuncanmaMSFT/docfx,hellosnow/docfx,pascalberger/docfx,superyyrrzz/docfx,superyyrrzz/docfx,928PJY/docfx,dotnet/docfx,pascalberger/docfx,hellosnow/docfx,DuncanmaMSFT/docfx,superyyrrzz/docfx,hellosnow/docfx,dotnet/docfx,dotnet/docfx