Fix errors in the description for installation on Windows (#17475)
Summary:
+ All quotes for ENV VARS are erroneous;
+ Toolset hasn't be specified;
+ Provide paths for all 3 Visual Studio 2017 products: Community/Professional/Enterprise.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/17475
Differential Revision: D14262968
Pulled By: soumith
fbshipit-source-id: c0504e0a6be9c697ead83b06b0c5cf569b5c8625
