Documentation on how to deploy with custom domain (#29)

* add DNS instructions
* route change
* Update for editing with kubectl

serving/DNS.md

@@ -0,0 +1,129 @@
+# Use a Custom Domain
+
+By default, Knative Serving routes use `demo-domain.com` as the default domain.
+The FDQN for a route by default is `{route}.{namespace}.{default-domain}`.
+
+To change the {default-domain} value there are a few steps involved:
+
+## Edit using kubectl
+
+1. Edit the domain configuration config-map to replace `demo-domain.com` 
+   with your own customer domain, for example `knative.dev`:
+
+```shell
+kubectl edit cm config-domain -n knative-serving
+```
+
+This will open your default text editor and allow you to edit the config map. 
+
+```yaml
+apiVersion: v1
+data:
+  # These are example settings of domain.
+  # prod-domain.com will be used for routes having app=prod.
+  prod-domain.com: |
+    selector:
+      app: prod
+
+  # Default value for domain, for routes that does not have app=prod labels.
+  # Although it will match all routes, it is the least-specific rule so it
+  # will only be used if no other domain matches.
+  demo-domain.com: |
+```
+
+Edit the file to replace `demo-domain.com` with the new domain you wish to use 
+and save your changes:
+
+```yaml
+apiVersion: v1
+data:
+  # These are example settings of domain.
+  knative.app: |
+    selector:
+      app: prod
+
+  # Default value for domain, for routes that does not have app=prod labels.
+  # Although it will match all routes, it is the least-specific rule so it
+  # will only be used if no other domain matches.
+  knative.dev: |
+```
+
+## Apply from a file
+
+You can also apply an updated domain configuration config-map:
+
+1. Create a new file, `config-domain.yaml` and paste the following text,
+   replacing the `prod-domain.com` and `demo-domain.com` values with the new
+   domain you want to use:
+
+    ```yaml
+    apiVersion: v1
+    kind: ConfigMap
+    metadata:
+      name: config-domain
+      namespace: knative-serving
+    data:
+      # These are example settings of domain.
+      # prod-domain.com will be used for routes having app=prod.
+      prod-domain.com: |
+        selector:
+          app: prod
+      # Default value for domain, for routes that does not have app=prod labels.
+      # Although it will match all routes, it is the least-specific rule so it
+      # will only be used if no other domain matches.
+      demo-domain.com: |
+```
+
+2. Apply updated domain configuration to your cluster:
+
+  ```shell
+  kubectl apply -f config-domain.yaml
+  ```
+
+## Deploy an application
+
+> If you have an existing deployment, Knative will reconcile the change made to
+> the configuration map and automatically update the host name for all deployed
+> services and routes.
+
+
+Deploy an app to your cluster as normal. For example, if you use the 
+[`helloworld-go`](./samples/helloworld-go/README.md) sample app, when the 
+ingress is ready, you'll see customized domain in HOSTS field together with 
+assigned IP address:
+
+```shell
+$ kubectl get ingress
+
+NAME                    HOSTS                                                                   ADDRESS        PORTS     AGE
+helloworld-go-ingress   helloworld-go.default.knative.dev,*.helloworld-go.default.knative.dev   35.237.28.44   80        2m
+```
+
+## Update your DNS records
+
+To enable the new custom domain to work in a browser, you need to update your
+DNS provider to point to the IP address for your service ingress.
+
+* Create an A record to point from the FDQN (shown as HOSTS in the ingress 
+  output) to the IP address listed:
+  
+    ```dns
+    helloworld-go.default.         59     IN     A   35.237.28.44
+    ```
+
+* Create a [wildcard record](https://support.google.com/domains/answer/4633759)
+  for the namespace and custom domain to the ingress IP Address. This will 
+  enable hostnames for multiple services in the same namespace to work without
+  creating additional DNS entries.
+
+    ```dns
+    *.default.                   59     IN     A   35.237.28.44
+    ```
+
+If you are using Google Cloud DNS, you can find step-by-step instructions
+in the [Cloud DNS quickstart](https://cloud.google.com/dns/quickstart).
+
+
+Once the domain update has propigated, you can then access your app using 
+the FQDN of the deployed route, for example
+`http://helloworld-go.default.knative.dev`