docs(upgrade): note on topic operator cleanup when upgrading with uni…

…directional mode (#9464)

Signed-off-by: prmellor <[email protected]>

documentation/assemblies/upgrading/assembly-upgrade-cluster-operator.adoc

@@ -33,6 +33,12 @@ The `helm upgrade` command does not upgrade the {HelmCustomResourceDefinitions}.
 Install the new CRDs manually after upgrading the Cluster Operator.
 You can access the CRDs from the {ReleaseDownload} or find them in the `crd` subdirectory inside the Helm Chart.
 
+== Migrating to unidirectional topic management
+
+When deploying the Topic Operator to manage topics, the Cluster Operator enables unidirectional topic management by default. 
+If you are switching from a version of Strimzi that used bidirectional topic management, there are some cleanup tasks to perform after upgrading the Cluster Operator.
+For more information, see xref:proc-changing-topic-operator-mode-{context}[].
+
 [id='con-upgrade-cluster-operator-unsupported-kafka-{context}']
 == Upgrading the Cluster Operator returns Kafka version error