Add listener documentation

guide/docs/extensions/listener.md

@@ -0,0 +1,47 @@
+## Register an event listener
+
+### Using the `listen` function
+
+You can register an event listener by calling the following function anywhere you want.
+
+```kotlin
+listen<EventClass> {
+    doSomething()
+}
+```
+
+The event instance will be passed in as `it`, but you can change this:
+
+```kotlin
+listen<PlayerMoveEvent> { moveEvent ->
+    moveEvent.player.kick("Do not move!")
+    broadcast("${moveEvent.player} moved :/")
+}
+```
+
+The `listen` function returns the `Listener` instance, which allows you to perform operations on it later.
+
+For example you could listen to a specific event temporarily:
+
+```kotlin
+val moveEventListener = listen<PlayerMoveEvent> {
+    it.player.kick("Do not move!")
+}
+
+// e.g. unregister the listener after some time
+taskRunLater(20 * 5) {
+    moveEventListener.unregister()
+}
+```
+
+### Registering an existing `Listener` instance
+
+There is an extension functions which registers a `Listener` instance:
+
+```kotlin
+listenerInstance.register()
+```
+
+## Unregister a `Listener`
+
+Just call `listenerInstance.unregister()`

guide/mkdocs.yml

@@ -31,3 +31,5 @@ nav:
       - Starting a new project: setup/project.md
       - Setup using Gradle: setup/gradle.md
       - Entrypoint to your plugin: setup/entrypoint.md
+  - Extensions:
+      - Event listener: extensions/listener.md