docs(index): include bootstrap in components example

The docs on the homepage for the component example requires bootstrap.css in
order to work properly. See angular/angular.js/#1258 for the original
discussion.

This ends up looking like this:
![angularjs superheroic javascript mvw framework 2014-01-20 07-00-06](https://f.cloud.github.com/assets/28543/1954647/2b8a4ee6-81db-11e3-8ecd-35c39ea6bf11.png)