Add example

example/example.dart

@@ -0,0 +1,15 @@
+import 'package:angel_framework/angel_framework.dart';
+import 'package:angel_mongo/angel_mongo.dart';
+import 'package:mongo_dart/mongo_dart.dart';
+
+main() async {
+  var app = new Angel();
+  Db db = new Db('mongodb://localhost:27017/local');
+  await db.open();
+
+  var service = app.use('/api/users', new MongoService(db.collection("users")));
+
+  service.afterCreated.listen((event) {
+    print("New user: ${event.result}");
+  });
+}