Clarify Kubernetes cluster creation sources

doc/user/project/clusters/add_remove_clusters.md

 # Adding and removing Kubernetes clusters
 
-GitLab can integrate with the following Kubernetes providers:
+GitLab offers integrated cluster creation for the following Kubernetes providers:
 
 - Google Kubernetes Engine (GKE).
 - Amazon Elastic Kubernetes Service (EKS).
 
+In addition, GitLab can integrate with any standard Kubernetes provider, either on-premise or hosted.
+
 TIP: **Tip:**
 Every new Google Cloud Platform (GCP) account receives [$300 in credit upon sign up](https://console.cloud.google.com/freetrial),
 and in partnership with Google, GitLab is able to offer an additional $200 for new GCP accounts to get started with GitLab's
@@ -360,18 +362,20 @@ to install some [pre-defined applications](index.md#installing-applications).
 
 ## Add existing cluster
 
-If you have either of the following types of clusters already, you can add them to a project:
+If you have an existing Kubernetes cluster, you can add it to a project, group, or instance.
+
+For more information, see information for adding an:
 
-- [Google Kubernetes Engine cluster](#existing-gke-cluster).
-- [Amazon Elastic Kubernetes Service](#existing-eks-cluster).
+- [Existing Kubernetes cluster](#existing-kubernetes-cluster).
+- [Existing Elastic Kubernetes Service cluster](#existing-eks-cluster).
 
 NOTE: **Note:**
 Kubernetes integration is not supported for arm64 clusters. See the issue
 [Helm Tiller fails to install on arm64 cluster](https://gitlab.com/gitlab-org/gitlab-foss/issues/64044) for details.
 
-### Existing GKE cluster
+### Existing Kubernetes cluster
 
-To add an existing GKE cluster to your project, group, or instance:
+To add a Kubernetes cluster to your project, group, or instance:
 
 1. Navigate to your:
    - Project's **Operations > Kubernetes** page, for a project-level cluster.

doc/user/project/clusters/index.md

@@ -96,8 +96,12 @@ to the first container in the first pod of your environment.
 
 ## Adding and removing clusters
 
-See [Adding and removing Kubernetes clusters](add_remove_clusters.md) for details on how to
-set up integrations with Google Cloud Platform (GCP) and Amazon Elastic Kubernetes Service (EKS).
+See [Adding and removing Kubernetes clusters](add_remove_clusters.md) for details on how
+to:
+
+- Create a cluster in Google Cloud Platform (GCP) or Amazon Elastic Kubernetes Service
+  (EKS) using GitLab's UI.
+- Add an integration to an existing cluster from any Kubernetes platform.
 
 ## Cluster configuration