Add default recipe

Hello!

I added a blank default recipe file (recipes/default.rb) so that your repository can be used as a cookbook by Berkshelf. By adding the blank file, Berkshelf "knows" how to download the repo for use in projects like my Linux virtual-machine builder (https://github.com/webcoyote/linux-vm). 

I also added tests/Gemfile so that the dependencies required for testing can be easily downloaded and installed in the event that they're not already on the system.

Finally, I ran your unit tests and nothing broke :)

Incidentally, your project is great! I was able to easily use your project with the Opscode "users" cookbook so that I could utilize their users::sysadmins recipe without requiring the use of Chef Server.

Thanks,

Pat