docs(events): describe the new events setup, update README.md files

Signed-off-by: Patrick Jungermann <Patrick.Jungermann@gmail.com>

plugins/events-node/README.md

@@ -1,3 +1,82 @@
-# plugin-events-node
+# `@backstage/plugin-events-node`
 
-Houses types and utilities for building events-related modules.
+This package defined basic types for event-based interactions inside of Backstage.
+
+Additionally, it provides the core event service `eventsServiceRef` of type `EventsService`
+with its default implementation that uses the `DefaultEventsService` implementation.
+
+`DefaultEventsService` is a simple in-memory implementation
+that requires the co-deployment of producers and consumers of events.
+
+## Installation
+
+Add `@backstage/plugin-events-node` as dependency to your plugin or plugin module package
+to which you want to add event support.
+
+Use `eventsServiceRef` as a dependency at your plugin or plugin module.
+
+### Legacy Backend System
+
+Create an `EventsService` instance and add it to the environment.
+
+```ts
+// packages/backend/src/plugins/events.ts
+import { DefaultEventsService } from '@backstage/plugin-events-node';
+
+// ...
+
+function makeCreateEnv(config: Config) {
+  // ...
+  const eventsService = DefaultEventsService.create({ logger: root });
+  // ...
+  return (plugin: string): PluginEnvironment => {
+    // ...
+    return {
+      // ...
+      events: eventsService,
+      // ...
+    };
+  };
+}
+```
+
+Use the `events` from the `PluginEnvironment` as desired:
+
+```ts
+// packages/backend/src/plugins/events.ts
+export default async function createPlugin(
+  env: PluginEnvironment,
+): Promise<Router> {
+  // ...
+  env.events; // ...
+  // ...
+}
+```
+
+## Use Case
+
+### Exchange service implementation
+
+Create your custom service factory implementation:
+
+```ts
+import { eventsServiceRef } from '@backstage/plugin-events-node';
+// ...
+export const customEventsServiceFactory = createServiceFactory({
+  service: eventsServiceRef,
+  deps: {
+    // add needed dependencies here
+  },
+  async factory({ logger }) {
+    // add your custom logic here
+    return customEventsService;
+  },
+});
+```
+
+and your custom implementation:
+
+```diff
+// packages/backend/src/index.ts
++  backend.add(customEventsServiceFactory());
+```