update readme: example section

Author: maroodb

README.md

@@ -33,3 +33,25 @@ implementation group: 'io.github.maroodb', name: 'simple-event', version: '1.0.1
     ...
 }
 ```
+
+## Example
+
+```
+
+var simpleEvent = new SimpleEvent<String>();
+
+var observable = simpleEvent.subscribe("MyTopic", (message) -> {
+    // do something with your message, or just print it!
+    System.out.print(message);
+});
+
+simpleEvent.publish("MyTopic", "Hello World!");
+
+// Unsubscribe from topic
+observable.unsubscribe();
+
+// nothing will happen
+simpleEvent.publish("MyTopic", "Hello World!");
+
+
+```