Plugin writing guide is in source but not visible on website

At some point a lot of the docs were deleted and simplified. The plugin writing stuff is still here at https://github.com/gocd/developer.go.cd/tree/master/source/writing_go_plugins but is not accessible and indexed off the main page.

Need to figure out if this is still relevant/useful and how it relates to the stuff at https://plugin-api.gocd.org/current/plugin-structure/#dependencies