Add an example for accordion on both small and large screens

If you want accordion functionality on both small and large screens, without tabs, the `accordion` class is required. Without the accordion class, the [**javascript**](https://github.com/zurb/foundation/blob/master/js/foundation/foundation.section.js#L95) will add top padding to the section element.
Merge pull request #1891 from simshaun/patch-2

Add an example for accordion on both small and large screens