Recommend SitePrism for acceptance test

[SitePrism](https://github.com/natritmeyer/site_prism) is a simple, but powerful DSL for something called [Page Objects](https://gist.github.com/gsmendoza/6050250).

SitePrism allows to easily define pages, sections and elements, works perfectly with capybara and rspec matchers and makes life simpler.

You can find some [example usage](https://github.com/hungryzi/ember-admin/tree/master/spec/features/support) on github already.

/cc @Ostrzy @teamon @chytreg @sheerun @szajbus @jcieslar