Update install instructions for eventing and eventing-sources. (#558)

* Switch install instructions to use a packaged release.

Signed-off-by: Evan Anderson <evan.k.anderson@gmail.com>

* Further fix eventing install based on discovered dependencies.

Signed-off-by: Evan Anderson <evan.k.anderson@gmail.com>

* Quick Overview section edit

I tried to quickly create sections and organize the info. PTAL at the edits to the design goals for technical accuracy.

* Events -> Eventing

eventing/README.md

@@ -1,25 +1,28 @@
 # Knative Eventing
 
-Knative Eventing is a system which is designed to address a common need for
+Knative Eventing is a system that is designed to address a common need for cloud native development and 
-cloud native development:
+provides composable primitives to enable late-binding event sources and event consumers.
 
-1.  Services are loosely coupled during development and deployed independently
+## Design overview
-    on a variety of platforms (Kubernetes, VMs, SaaS or FaaS).
-1.  A producer can generate events before a consumer is listening, and a
-    consumer can express an interest in an event or class of events that is not
-    yet being produced.
-1.  Services can be connected to create new applications
-    - without modifying producer or consumer.
-    - with the ability to select a specific subset of events from a particular
-      producer
 
-The above concerns are consistent with the
+Knative Eventing is designed around the following goals:
-[design goals of CloudEvents](https://github.com/cloudevents/spec/blob/master/spec.md#design-goals),
+
-a common specification for cross-service interoperability being developed by the
+1. Knative Eventing services are loosely coupled. These services can be developed and deployed independently on,
-CNCF Serverless WG.
+   and across a variety of platforms (for example Kubernetes, VMs, SaaS or FaaS).
+1. Event producers and event sources are independent. Any producer (or source), can generate events 
+   before there are active event consumers that are listening. Any event consumer can express interest in an 
+   event or class of events, before there are producers that are creating those events.
+1. Other services can be connected to the Eventing system. These services can perform the following functions:
+   - Create new applications without modifying the event producer or event consumer. 
+   - Select and target specific subsets of the events from thier producers.
+1. Ensure cross-service interoperability. Knative Eventing is consistent with the 
+   [CloudEvents](https://github.com/cloudevents/spec/blob/master/spec.md#design-goals)
+   specification that is developed by the [CNCF Serverless WG](https://lists.cncf.io/g/cncf-wg-serverless).
+
+### Event consumers
 
 To enable delivery to multiple types of Services, Knative Eventing defines two
-generic interfaces which multiple Kubernetes resources can implement:
+generic interfaces that can be implemented by multiple Kubernetes resources:
 
 1. **Addressable** objects are able to receive and acknowledge an event
    delivered over HTTP to an address defined in their `status.address.hostname`
@@ -31,6 +34,8 @@ generic interfaces which multiple Kubernetes resources can implement:
    returned events may be further processed in the same way that events from an
    external event source are processed.
 
+### Event channels and subscriptions
+
 Knative Eventing also defines a single event forwarding and persistence layer,
 called a
 [**Channel**](https://github.com/knative/eventing/blob/master/pkg/apis/eventing/v1alpha1/channel_types.go#L36).
@@ -43,29 +48,43 @@ This allows message delivery in a cluster to vary based on requirements, so that
 some events might be handled by an in-memory implementation while others would
 be persisted using Kafka or NATS Streaming.
 
+### Future design goals
+
 The focus for the next Eventing release will be to enable easy implementation of
 event sources. Sources manage registration and delivery of events from external
 systems using Kubernetes
 [Custom Resources](https://kubernetes.io/docs/concepts/extend-kubernetes/api-extension/custom-resources/).
+Learn more about Eventing development in the [Eventing work group](https://github.com/knative/docs/blob/master/community/WORKING-GROUPS.md#events).
 
 ## Installation
 
-You can install the core Knative Eventing (which provides an in-memory
+Knative Eventing currently requires Knative Serving and Istio version 1.0 or
-ChannelProvisioner) and the core sources (which provides the Kubernetes Events
+later installed. Use this command to install the version of Istio which is
-and "Container" Sources) with the following commands:
+tested with Knative:
 
-<!-- TODO(evankanderson): Switch to a numbered release when available. -->
+```shell
-
+kubectl apply --filename https://raw.githubusercontent.com/knative/serving/v0.2.2/third_party/istio-1.0.2/istio.yaml
-```bash
+kubectl apply --filename https://github.com/knative/serving/releases/download/v0.2.2/release.yaml
-kubectl apply --filename https://storage.googleapis.com/knative-releases/eventing/latest/release.yaml
-kubectl apply --filename https://storage.googleapis.com/knative-releases/eventing-sources/latest/release.yaml
 ```
 
-In addition to the core sources, you can also use GCP PubSub as a source with
+You can install the core Knative Eventing (which provides an in-memory
-the following yaml:
+ChannelProvisioner) and the core sources (which provides the Kubernetes Events,
+GitHub, and "Container" Sources) with the following commands:
 
 ```bash
-kubectl apply --filename https://storage.googleapis.com/knative-releases/eventing-sources/latest/release-with-gcppubsub.yaml
+kubectl apply --filename https://github.com/knative/eventing/releases/download/v0.2.0/release.yaml
+kubectl apply --filename https://github.com/knative/eventing-sources/releases/download/v0.2.0/release.yaml
+```
+
+In addition to the core sources, you can also use GCP PubSub as a source by
+creating a secret with the name `gcppubsub-source-key` with a `key.json` value
+and loading the released source yaml (the `-with-gcppubsub` release includes all
+the above sources, and adds GCP PubSub, which requires the listed secret):
+
+```bash
+kubectl create namespace knative-sources
+kubectl --namespace knative-sources create secret generic gcppubsub-source-key --from-literal=key.json=''
+kubectl apply --filename https://github.com/knative/eventing-sources/releases/download/v0.2.0/release-with-gcppubsub.yaml
 ```
 
 This document will be updated as additional sources (which are custom resource