Update layout.jade from doctype 5 to doctype html

I cloned this project and got an error when running it out of the box; had to fix this issue before it would fully work.

![screenshot 2014-02-26 16 27 47](https://f.cloud.github.com/assets/1016999/2275900/3aa10eb4-9f2d-11e3-81d9-97dbaf9591ad.png)

Also, unrelated, you may want to include in the installation steps something about updating your data center ('dc') in mailchimp.js - we are us5 but it specifies us1 by default.