[cookbook] Added cookbook for notifying users of updated application versions

I'm not sure how idiomatic this is but you could do something like
```js
container.lookup('controller:application').send('newVersionAvailable');
```
which would make `newVersionAvailable` into an action/event against the application controller, which if not handled in the controller would bubble up into the router. 

The downside of this approach is if it triggers before Ember has loaded the first time you'll get an error like
```js
Error: Can't trigger action 'newVersionAvailable' because your app hasn't finished transitioning into its first route. To trigger an action on destination routes during a transition, you can call `.send()` on the `Transition` object passed to the `model/beforeModel/afterModel` hooks.
```