docs: Add info regarding Pf4j documentation and request pages, as well as add minigame example to list of addons

breaking: Remove start-script related code as this option is no longer available in ServerPackCreator

chore: Add example output produces by this example addon when using it with a dev build of ServerPackCreator 3.x.x

Initial commit. Provide base example of an addon for ServerPackCreator with documentation and tests.