Clarify PSP/PV interaction (#15756)

content/en/docs/concepts/policy/pod-security-policy.md

@@ -420,6 +420,11 @@ The **recommended minimum set** of allowed volumes for new PSPs are:
 - secret
 - projected
 
+{{< warning >}}
+PodSecurityPolicy does not limit the types of `PersistentVolume` objects that may be referenced by a `PersistentVolumeClaim`.
+Only trusted users should be granted permission to create `PersistentVolume` objects.
+{{< /warning >}}
+
 **FSGroup** - Controls the supplemental group applied to some volumes.
 
 - *MustRunAs* - Requires at least one `range` to be specified. Uses the