removing annotation does not remove broker (#1620)

* removing annotation does not remove broker

* address feedback

docs/eventing/broker-trigger.md

@@ -116,6 +116,19 @@ namespace.
 kubectl -n default get broker default
 ```
 
+*NOTE* `Broker`s created due to annotation will not be removed if you
+remove the annotation. For example, if you annotate the namespace,
+which will then create the `Broker` as described above. If you now
+remove the annotation, the `Broker` will not be removed, you have
+to manually delete it.
+
+For example, to delete the injected Broker from the foo namespace:
+
+```shell
+kubectl -n foo delete broker default
+```
+
+
 #### Manual Setup
 
 In order to setup a `Broker` manually, we must first create the required