OSDOCS-4115: adds Hawkular migration limitation to monitoring considerations

Author: JoeAldinger

migrating_from_ocp_3_to_4/planning-migration-3-4.adoc

@@ -211,7 +211,7 @@ For more information, see xref:../authentication/managing-security-context-const
 [id="migration-preparing-monitoring"]
 === Monitoring considerations
 
-Review the following monitoring changes to consider when transitioning from {product-title} 3.11 to {product-title} {product-version}.
+Review the following monitoring changes when transitioning from {product-title} 3.11 to {product-title} {product-version}. You cannot migrate Hawkular configurations and metrics to Prometheus.
 
 [discrete]
 ==== Alert for monitoring infrastructure availability