Display directory layouts with tree(1)

If you have the examples directories around, you can easily display their contents with `tree`. It comes with most Linux distributions and can be easily installed on OSX with `brew install tree`.

I kinda like the output it produces and it can help with the consistent representation of directory structures, such as those in the guide.

You can check out my [fork](https://github.com/gsamokovarov/angularjs-style-guide/tree/tree-layout) for a visual preview.