initial delivery options doc (#1994)

* initial delivery options doc

* fix typos

docs/eventing/event-delivery.md

@@ -0,0 +1,64 @@
+---
+title: "Event Delivery"
+weight: 20
+type: "docs"
+---
+
+## Overview
+
+Knative Eventing provides various configuration parameters to control the delivery
+of events in case of failure. For instance, you can decide to retry sending events
+that failed to be consumed, and if this didn't work you can decide to forward those
+events to a dead letter sink.
+
+## Configuring Subscription Delivery
+
+Knative Eventing offers fine-grained control on how events are delivered for each subscription by adding a `delivery` section. Consider this example:
+
+```yaml
+apiVersion: messaging.knative.dev/v1alpha1
+kind: Subscription
+metadata:
+  name: with-dead-letter-sink
+spec:
+  channel:
+    apiVersion: messaging.knative.dev/v1alpha1
+    kind: InMemoryChannel
+    name: default
+  delivery:
+    deadLetterSink:
+      ref:
+        apiVersion: serving.knative.dev/v1
+        kind: Service
+        name: error-handler
+  subscriber:
+    uri: http://doesnotexist.default.svc.cluster.local
+```
+
+The `deadLetterSink` specifies where to send events that failed be consumed by `subscriber`.
+
+## Common Delivery Parameters
+
+### deadLetterSink
+
+When present, events that failed to be consumed are sent to the `deadLetterSink`.
+In case of failure, the event is dropped and an error is logged into the system.
+
+The `deadLetterSink` value must be a [Destination](https://godoc.org/knative.dev/pkg/apis/duck/v1#Destination).
+
+```yaml
+spec:
+  delivery:
+    deadLetterSink: <Destination>
+```
+
+## Channel Support
+
+The table below summarizes what delivery parameters are supported for each channel implementation.
+
+| Channel Type | Supported Delivery Parameters |
+| - | - |
+| In-Memory | `deadLetterSink` |
+| Kafka | none |
+| Natss | none |
+| GCP PubSub | none |