Update Prow setup for a new org
Add instructions for setting the Gubernator PR Dashboard webhook.
## Setting up Prow for a new organization
-1. In GitHub, add a [webhook](https://developer.github.com/webhooks/) to the org
- (or repo) that points to <http://prow.knative.dev/hook> and sends all events
- in `application/json` format. Ask one of the owners of knative/test-infra for
- the webhook secret.
+1. In GitHub, add the following [webhooks](https://developer.github.com/webhooks/)
+ to the org (or repo), in `application/json` format and for all events. Ask one
+ of the owners of knative/test-infra for the webhook secrets.
+
+ 1. <http://prow.knative.dev/hook> (for Prow)
+ 1. <https://github-dot-knative-tests.appspot.com/webhook> (for Gubernator PR
+ Dashboard)
1. Create a team called _Knative Prow Robots_, and make it an Admin of the org
(or repo).
