Bring back the walkthrough tutorial

This brings back the walkthrough, a couple notes : 

- I had to convert the original markdown manually to HTML, is that how it's supposed to work? I noticed there's no markdown source included for the other HTML files
- There's a layout issue, the screenshots vs code samples are no longer next to each other, compare http://webcache.googleusercontent.com/search?q=cache:kyktz_6jLXMJ:shoesrb.com/walkthrough+&cd=1&hl=en&ct=clnk&gl=de&client=ubuntu
- The old URL (/walkthrough) no longer works, it has a .html suffix now