added codio tutorial

@addyosmani we a) modified the Codio/Yeoman tutorial (https://github.com/codio/tutorial_yo_angular) to have it in sync with the latest Codelab page b) added a simple paragraph and link to the codelab page itself (this pr).

We'd be happy to put together others if you feel this approach is beneficial to readers and we'll keep an eye out for updates and be sure to keep it all in sync (Karma generator issues etc).