example of effects on single region

@testbrian, I think what @samccone is saying is:

```js
var ModalRegion = Region.extend({
  attachHtml: function(view){
    // Some effect to show the modal
  }
});

MyApp.addRegions({
  mainRegion: "#main-content",
  modal: "#modal-region",
  regionClass: ModalRegion
});
```

I personally think both are good approaches that should be documented. You'll have to check, but I bet we have documentation showing the regionClass example, so maybe we just need yours...