Install Script Edits

I corrected a small typo in the readme file.

In the latest releases the yeoman developer changed the paths to the
generators slightly. Also, os.exit() was causing an error if the
directory wasn't found, changed to use the sys library instead.

![Aww Yeah](http://i0.kym-cdn.com/photos/images/newsfeed/000/106/887/backpain-1292835351.jpg)