Add note for TechPreview fail message in PO

Author: adellape

modules/olm-installing-po-after.adoc

@@ -32,6 +32,17 @@ spec:
 ----
 $ oc apply -f cert-manager.yaml
 ----
++
+[NOTE]
+====
+If your cluster does not have the `TechPreviewNoUpgrades` feature set enabled, the object creation fails with the following message:
+
+[source,terminal]
+----
+error: resource mapping not found for name: "cert-manager" namespace: "" from "cert-manager.yaml": no matches for kind "PlatformOperator" in version "platform.openshift.io/v1alpha1"
+ensure CRDs are installed first
+----
+====
 
 .Verification