Update readme for vs15.7
Update readme for vs15.7

mono/msbuild,Microsoft/msbuild,AndyGerlicher/msbuild,chipitsine/msbuild,mono/msbuild,rainersigwald/msbuild,cdmihai/msbuild,Microsoft/msbuild,mono/msbuild,rainersigwald/msbuild,sean-gilliam/msbuild,rainersigwald/msbuild,AndyGerlicher/msbuild,cdmihai/msbuild,jeffkl/msbuild,AndyGerlicher/msbuild,AndyGerlicher/msbuild,Microsoft/msbuild,cdmihai/msbuild,jeffkl/msbuild,sean-gilliam/msbuild,chipitsine/msbuild,jeffkl/msbuild,sean-gilliam/msbuild,chipitsine/msbuild,Microsoft/msbuild,rainersigwald/msbuild,sean-gilliam/msbuild,chipitsine/msbuild,mono/msbuild,cdmihai/msbuild,jeffkl/msbuild