add description for service account token

ref:kubernetes/kubernetes#63819
    #9182

Author: WanLinghao

content/en/docs/tasks/configure-pod-container/configure-projected-volume-storage.md

@@ -8,7 +8,13 @@ weight: 70
 ---
 
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-This page shows how to use a [`projected`](/docs/concepts/storage/volumes/#projected) volume to mount several existing volume sources into the same directory. Currently, `secret`, `configMap`, and `downwardAPI` volumes can be projected.
+This page shows how to use a [`projected`](/docs/concepts/storage/volumes/#projected) volume to mount
+several existing volume sources into the same directory. Currently, `secret`, `configMap`, `downwardAPI`,
+and `serviceAccountToken` volumes can be projected.
+
+{{< note >}}
+`serviceAccountToken` is not a volume type.
+{{< /note >}}
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content/en/docs/tasks/configure-pod-container/configure-service-account.md

@@ -248,4 +248,13 @@ spec:
 TODO: Test and explain how to use additional non-K8s secrets with an existing service account.
 -->
 
-{{% /capture %}}
+## Service Account Volume Projection
+
+Kubernetes 1.11 and higher supports a new way to project a service account token into a Pod.
+You can specify a token request with audiences, expirationSeconds. The service account token
+becomes invalid when the Pod is deleted. A Projected Volume named
+[ServiceAccountToken](/docs/concepts/storage/volumes/#projected) requests and stores the token.
+
+{{% /capture %}}
+
+