Include README, CHANGELOG and other static files from the code repo

[flavorjones]

There are some valuable docs in the code repo (http://github.com/sparklemotion/nokogiri) that would be good to include in this docs site.

• [x] figure out navigation
• [x] write some code to import files from a local-disk clone
• [x] write some more codes to make those docs part of the deployment