add note in kubernetes section for cluster domain

Author: maltesander

modules/ROOT/pages/kubernetes/index.adoc

@@ -77,3 +77,8 @@ Kubernetes control plane is running at https://127.0.0.1:6443
 CoreDNS is running at https://127.0.0.1:6443/api/v1/namespaces/kube-system/services/kube-dns:dns/proxy
 Metrics-server is running at https://127.0.0.1:6443/api/v1/namespaces/kube-system/services/https:metrics-server:https/proxy
 ----
+
+=== Configuring the cluster domain
+
+In case a non-default cluster domain is used as described in https://kubernetes.io/docs/tasks/administer-cluster/dns-custom-nameservers/[Customizing DNS Service],
+Stackable operators can be configured accordingly. This is described in detail in this guide xref:cluster-domain.adoc[Configuring the Kubernetes cluster domain].