Candlepin documentation is split into three major pieces. A Jekyll based web site http://candlepinproject.org/, JavaDoc that is currently only in the source code and REST API that is being hosted on http://candlepinproject.org/ and is auto-generated by so called API Crawler (Java project in server’s code base)
When you need to submit new documentation, you should clone sources of the site from Github repo and issue a Pull Request. After your pull request is merged, the new site content is automatically published to http://candlepinproject.org/
While preparing the Pull Request with changes to the documentation you should use local Jekyll instance to see your changes to the documentation. See README.md file in site’s sources.