Here are links to documentation for open source yorick plugins and packages which are not part of the main distribution. These packages add functionality to yorick; because they are open source, you can use their source code as templates for creating your own extensions to yorick.
To create documentation for your own package, clone the yorick-doc git repository, then run the ydoc.pl git script on your yorick plugin tree. If you publish your yorick-doc generated website, you can add its URL to the following list in your copy of the yorick-doc repo, and issue a pull request to have your documentation appear here.