backport: Document olm-deployer and fix secret/listener-operator memory docs (#912) (#913)

Author: sbernauer

modules/ROOT/pages/kubernetes/openshift.adoc

@@ -6,6 +6,10 @@ SDP operators are certified for the OpenShift platform and can be installed from
 
 IMPORTANT: OpenShift installations with FIPS mode enabled are not supported. This is because neither the SDP operators, nor the supported Apache products are FIPS-compliant.
 
+IMPORTANT: The operators deployed with OLM might have higher memory requests (and limits) compared to our Helm charts, as we have seen typical production OpenShift clusters being larger than typical non-Openshift clusters.
+The reason is that memory usage of some of our operators scales with the number of objects in your Kubernetes cluster.
+However, you can fine-tune the operator memory requirements using a custom Subscription object as described below, so this note is only about the default resources!
+
 == Customizing operator installations
 
 As described in the https://github.com/operator-framework/operator-lifecycle-manager/blob/master/doc/design/subscription-config.md[Openshift Subscription documentation{external-link-icon}^] you can configure the deployed operators.
@@ -52,7 +56,12 @@ spec:
         value: kafka-namespace
 ----
 
-IMPORTANT: The described configuration mechanism currently does not work for secret and listener-operator due to restrictions on deploying DaemonSets.
+=== secret and listener-operator
+
+The secret and listener operator are not deployed by OLM directly but rather by a helper tool called `olm-deployer`. This tool is needed to work around some OLM limitations that prevent it from directly installing these operators.
+In this case, `olm-deployer` takes **it's own** resource requests and applies them to all containers on the `DaemonSets` of these operators..
+
+This allows you to customize the resources of the DaemonSet in the same way as for the other operators - but doesn't allow individual resources for each container.
 
 == Security context constraints