ARO VNet also needs to be updated in the MachineSet YAML manifest

ARO VNet also needs to be updated in the MachineSet YAML manifest by the user. Modified the manifest so that a placeholder is seen to update the ARO VNet name.

Author: saurabhvartak1982

articles/openshift/howto-infrastructure-nodes.md

@@ -142,7 +142,7 @@ spec:
           userDataSecret:
             name: worker-user-data 
           vmSize: <Standard_E4s_v5, Standard_E8s_v5, Standard_E16s_v5>
-          vnet: aro-vnet 
+          vnet: <VNET_NAME> 
           zone: <ZONE>
       taints: 
       - key: node-role.kubernetes.io/infra