setting a custom resource as sink doc (#3502)

* First pass to setting resource as sink

* Adding more clarity on example

docs/eventing/sink/_index.md

@@ -44,6 +44,37 @@ spec:
       name: my-kafka-sink
 ```
 
+## Setting up a Custom Resource to be used as a sink
+To allow a Custom Resource to act as a sink for events, there are two things needed: 
+
+#### 1. Make the resource Addressable
+To make a Custom Resource Addressable, it needs to contain a `status.address.url`. More information about [Addressable resources](https://github.com/knative/specs/blob/main/specs/eventing/interfaces.md#addressable).
+
+#### 2. Create an addressable-resolver ClusterRole
+An addressable-resolver ClusterRole is needed in order to obtain the necessary RBAC rules for the sink to receive events.
+
+For example, we can create a `kafkasinks-addressable-resolver` ClusterRole to allow `get`, `list`, and `watch` access to `kafkasinks` and `kafkasinks/status`
+```yaml
+kind: ClusterRole
+apiVersion: rbac.authorization.k8s.io/v1
+metadata:
+  name: kafkasinks-addressable-resolver
+  labels:
+    kafka.eventing.knative.dev/release: devel
+    duck.knative.dev/addressable: "true"
+# Do not use this role directly. These rules will be added to the "addressable-resolver" role.
+rules:
+  - apiGroups:
+      - eventing.knative.dev
+    resources:
+      - kafkasinks
+      - kafkasinks/status
+    verbs:
+      - get
+      - list
+      - watch
+ ```
+
 ## Knative Sinks
 
 | Name | Maintainer | Description |