Add run.cmd for Windows

Hi Doug,

I added a `run.cmd` file for use by those developing on Windows. Its behavior should be the same as the bash script you provided. I also modified the `README` in a couple of places include its usage instructions.

Thanks for providing this sample app. It's been a big help to me in picking up atom-shell development.

Sincerely,
David Holt
dholtdev@gmail.com