Add explicit assumptions before the installation steps (elastic#5455)

* Add explicit note before install steps

* More edits

* Integrate Peter's feedback

docs/quickstart.asciidoc

@@ -29,18 +29,17 @@ include::supported-versions.asciidoc[]
 [id="{p}-deploy-eck"]
 == Deploy ECK in your Kubernetes cluster
 
-IMPORTANT: Check the <<{p}-upgrading-eck,upgrade notes>> first if you are attempting to upgrade an existing ECK deployment.
+Things to consider before you start:
 
-[NOTE]
-====
+* For this quickstart guide, your Kubernetes cluster is assumed to be already up and running. Before you proceed with the ECK installation, make sure you check the link:k8s-quickstart.html[supported versions].
 
 * If you are using GKE, make sure your user has `cluster-admin` permissions. For more information, check link:https://cloud.google.com/kubernetes-engine/docs/how-to/role-based-access-control#iam-rolebinding-bootstrap[Prerequisites for using Kubernetes RBAC on GKE].
 
 * If you are using Amazon EKS, make sure the Kubernetes control plane is allowed to communicate with the Kubernetes nodes on port 443. This is required for communication with the Validating Webhook. For more information, check link:https://docs.aws.amazon.com/eks/latest/userguide/sec-group-reqs.html[Recommended inbound traffic].
 
 * Refer to <<{p}-installing-eck>> for more information on installation options.
 
-====
+IMPORTANT: Check the <<{p}-upgrading-eck,upgrade notes>> if you are attempting to upgrade an existing ECK deployment.
 
 . Install link:https://kubernetes.io/docs/concepts/extend-kubernetes/api-extension/custom-resources/[custom resource definitions]:
 +