Updating README.md

Author: DaWyz

packages/@aws-cdk/aws-events/README.md

@@ -186,3 +186,17 @@ bus.archive('MyArchive', {
   retention: cdk.Duration.days(365),
 });
 ```
+
+## Granting PutEvents to an existing EventBus
+
+To import an existing EventBus into your CDK application, use `EventBus.fromEventBusArn` or `EventBus.fromEventBusAttributes`
+factory method.
+
+Then, you can use the `grantPut` method to grant `event:PutEvents` to the eventBus.
+
+```ts
+const eventBus = EventBus.fromEventBusArn(this, 'ImportedEventBus', 'arn:aws:events:us-east-1:111111111:event-bus/my-event-bus');
+
+// now you can just call methods on the eventbus
+eventBus.grantPut(lambdaFunction);
+```