add note, regarding example requirement for nfs helper /sbin/mount.nfs (#19774)

Author: spurin

content/en/docs/concepts/storage/persistent-volumes.md

@@ -312,6 +312,10 @@ spec:
     server: 172.17.0.2
 ```
 
+{{< note >}}
+Helper programs relating to the volume type may be required for consumption of a PersistentVolume within a cluster.  In this example, the PersistentVolume is of type NFS and the helper program /sbin/mount.nfs is required to support the mounting of NFS filesystems.
+{{< /note >}}
+
 ### Capacity
 
 Generally, a PV will have a specific storage capacity.  This is set using the PV's `capacity` attribute.  See the Kubernetes [Resource Model](https://git.k8s.io/community/contributors/design-proposals/scheduling/resources.md) to understand the units expected by `capacity`.