Make it clear that documentjs is watching for changes

DocumentJS should log a message to the terminal letting them know that files are being watched for changes and will re-generate the docs. Otherwise it appears that the `documentjs` command has hung.

Following the [DocumentCSS guide](http://documentcss.com/docs/index.html), the user is prompted to use `documentjs -w`. When you do that you're left with the message `Generating styles at styleguide` and nothing else.