We have not managed to update the docs yet, I’m afraid, so currently, there’s only the source code to the rescue and an example plugin file:
Plugin registry: https://gist.github.com/bastianallgeier/38f895b32b71e8e2b2f3844e38df5489
For the component architecture, you can have a look at the Twig plugin by @fvsch: Twig plugin (Kirby 2.3+) as an example.