Update grunt command on windows

[xiaoyu3x]

update README.md

[gabrielschulhof]

TBH I don't want to document that. grunt test should work, even on Windows, and I've seen it work. It just doesn't work on Appveyor, which is why I've adjusted the appveyor.yml file. If grunt test doesn't work, I want people to see it fail, because it might prompt them to find out what needs to be done to make it work.

[coveralls]

Coverage remained the same at 86.951% when pulling f9c71a8 on xiaoyu3x:update-readme into 257dde7 on otcshare:master.