Support Windows OS based contributors #2855

I'd like to keep the ball rolling to make it easier for contributors on Windows based machines to help out on CRA. We can use this issue to keep track of the portions of the dev experience that don't work well or at all on Windows. @cr101, @Dubes, or any other Windows contributors feel free to suggest improvements.

• Port cra.sh to support npm run create-react-app my-app
• Documentation to help windows contributors