Quick reference takeaways

Hi RailsBridge. I volunteered to teach for the first time on Jan 20th, on the frontend curriculum, and had a really fun time. I thought it'd be awesome for students to have a quick reference sheet that highlights some of the things they learned, and so I worked on that with input from fellow Carbon Fivers: @blakeeb, @jonah-carbonfive, and particularly @vhmartini who was a student that Saturday.

This pull request adds a reference for HTML and a link to it add the end of the curriculum. I added it as an HTML file under public/frontend/quick-reference, since it's a reference rather than part of the goal/step/explanation curriculum.

![Screen Shot 2013-01-29 at 10 00 34 AM](https://f.cloud.github.com/assets/472778/107954/d9869880-6a3d-11e2-8ab8-e1d9d1bca757.png)

Also, I noticed it automatically shows up in the table of contents. Not sure if that's desirable or not. If not, a pointer on how to remove it would be great since, like I mentioned, it just showed up automatically.

Thanks!