Help tab

An idea for how to describe the shortcodes to users. Creates a button alongside the "Add Media" button which pops up an automatically HTML-ified version of README.md. This way we don't have to update two different help files, and the information is easily available to the user.

What do you think?

![screen shot 2013-09-14 at 7 55 03 am](https://f.cloud.github.com/assets/2457670/1143337/8ad506f4-1d34-11e3-86f4-f958f392a871.png)

And becuase I'm terrible at branching this pull request also includes my Jumbotron code which closes #11.