add readme info about using secret for registry passwords

stable/spinnaker/README.md

@@ -60,6 +60,32 @@ for Spinnaker. If you want to add arbitrary clusters need to do the following:
       deploymentContext: my-context
     ```
 
+## Specifying Docker Registries and Valid Images (Repositories)
+
+Spinnaker will only give you access to Docker images that have been whitelisted, if you're using a private registry or a private repository you also need to provide credentials.  Update the following values of the chart to do so:
+
+    ```yaml
+    dockerRegistries:
+    - name: dockerhub
+      address: index.docker.io
+      repositories:
+        - library/alpine
+        - library/ubuntu
+        - library/centos
+        - library/nginx
+    # - name: gcr
+    #   address: https://gcr.io
+    #   username: _json_key
+    #   password: '<INSERT YOUR SERVICE ACCOUNT JSON HERE>'
+    #   email: [email protected]
+    ```
+
+You can provide passwords as a Helm value, or you can use a pre-created secret containing your registry passwords.  The secret should have an item per Registry in the format: `<registry name>: <password>`. In which case you'll specify the secret to use in `dockerRegistryAccountSecret` like so:
+
+    ```yaml
+    dockerRegistryAccountSecret: myregistry-secrets
+    ```
+
 ## Customizing your installation
 
 ### Manual

stable/spinnaker/templates/configmap/halyard-config.yaml

@@ -56,7 +56,6 @@ data:
     {{ end }}
 
     # Docker Registry
-
     $HAL_COMMAND config provider docker-registry enable
     {{- range $index, $registry := .Values.dockerRegistries }}