clarify network policy implementations

setup/kubernetes/azure.md

@@ -78,6 +78,16 @@ az aks create \
   --network-policy "calico"
 ```
 
+> [AKS offers built-in
+support](https://docs.microsoft.com/en-us/azure/aks/use-network-policies#create-an-aks-cluster-and-enable-network-policy)
+for the
+[Calico](https://docs.projectcalico.org/getting-started/kubernetes/managed-public-cloud/gke)
+network policy engine, and you can opt-in by including the `--network-policy
+"calico"` flag.
+>
+> However, you can only choose Calico as your network policy option when you
+create the cluster; you cannot enable Calico on an existing cluster.
+
 This process might take some time (~5-20 minutes), but if you're successful,
 Azure returns a JSON object with your cluster information.
 

setup/kubernetes/google.md

@@ -46,6 +46,10 @@ clusters create "$NEW_CLUSTER_NAME" \
    --max-nodes "8"
 ```
 
+> The example above includes the use of the `enable-network-policy` flag, which will
+result in the [creation of a Calico
+cluster](https://kubernetes.io/docs/tasks/administer-cluster/network-policy-provider/calico-network-policy/).
+
 To create clusters capable of supporting use of the
 [CVMs](../../admin/environment-management/cvms.md) deployment option: