It is a documentations for Treehouses.io which backed by Open Learning Exchange. The contribution to this repository is very simple. You just need to change existing markdown or create a new one if necessary. All the table-of-contents-like index are stored in SUMMARY.md and the home is stored in README.md.
Basically to deploy new changes you just need to run the publish_gitbook.sh. It will update the gh-pages branch for you and it will trigger GitHub Pages to recompile the static site.