Change EnvVarSource.FieldPath -> FieldRef and add example

examples/downward-api/README.md

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+# Downward API example
+
+Following this example, you will create a pod with a containers that consumes the pod's name and
+namespace using the downward API.
+
+## Step Zero: Prerequisites
+
+This example assumes you have a Kubernetes cluster installed and running, and that you have
+installed the ```kubectl``` command line tool somewhere in your path. Please see the [getting
+started](../../docs/getting-started-guides) for installation instructions for your platform.
+
+## Step One: Create the pod
+
+Containers consume the downward API using environment variables.  The downward API allows
+containers to be injected with the name and namespace of the pod the container is in.
+
+Use the `examples/secrets/secret-pod.yaml` file to create a Pod with a container that consumes the
+downward API.
+
+```shell
+$ kubectl create -f examples/downward-api/dapi-pod.yaml
+```
+
+### Examine the logs
+
+This pod runs the `env` command in a container that consumes the downward API.  You can grep
+through the pod logs to see that the pod was injected with the correct values:
+
+```shell
+$ kubectl log dapi-test-pod | grep POD_
+2015-04-30T20:22:18.568024817Z POD_NAME=dapi-test-pod
+2015-04-30T20:22:18.568087688Z POD_NAMESPACE=default
+```

examples/downward-api/dapi-pod.yaml

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+apiVersion: v1beta3
+kind: Pod
+metadata:
+  name: dapi-test-pod
+spec:
+  containers:
+    - name: test-container
+      image: gcr.io/google_containers/busybox
+      command: [ "/bin/sh", "-c", "env" ]
+      env:
+        - name: POD_NAME
+          valueFrom:
+            fieldRef:
+              fieldPath: metadata.name
+        - name: POD_NAMESPACE
+          valueFrom:
+            fieldRef:
+              fieldPath: metadata.namespace
+  restartPolicy: Never