Add info on creating your own k8s cluster from the cluster page

doc/user/project/clusters/index.md

-# Connecting GitLab with GKE
+# Connecting GitLab with a Kubernetes cluster
 
 > [Introduced](https://gitlab.com/gitlab-org/gitlab-ce/issues/35954) in 10.1.
 
 CAUTION: **Warning:**
 The Cluster integration is currently in **Beta**.
 
-Connect your project to Google Container Engine (GKE) in a few steps.
-
 With a cluster associated to your project, you can use Review Apps, deploy your
-applications, run your pipelines, and much more in an easy way.
+applications, run your pipelines, and much more, in an easy way.
+
+Connect your project to Google Container Engine (GKE)  or your own Kubernetes
+cluster in a few steps.
 
 NOTE: **Note:**
 The Cluster integration will eventually supersede the
@@ -30,31 +31,41 @@ prerequisites must be met:
 - You must have Master [permissions] in order to be able to access the **Cluster**
   page.
 
-If all of the above requirements are met, you can proceed to add a new cluster.
+If all of the above requirements are met, you can proceed to add a new GKE
+cluster.
 
 ## Adding a cluster
 
 NOTE: **Note:**
 You need Master [permissions] and above to add a cluster.
 
+There are two options when adding a new cluster; either use Google Container
+Engine (GKE) or provide the credentials to your own Kubernetes cluster.
+
 To add a new cluster:
 
-1. Navigate to your project's **CI/CD > Cluster** page.
-1. Connect your Google account if you haven't done already by clicking the
-   "Sign-in with Google" button.
-1. Fill in the requested values:
-  - **Cluster name** (required) - The name you wish to give the cluster.
-  - **GCP project ID** (required) - The ID of the project you created in your GCP
-    console that will host the Kubernetes cluster. This must **not** be confused
-    with the project name. Learn more about [Google Cloud Platform projects](https://cloud.google.com/resource-manager/docs/creating-managing-projects).
-  - **Zone** - The zone under which the cluster will be created. Read more about
-    [the available zones](https://cloud.google.com/compute/docs/regions-zones/).
-  - **Number of nodes** - The number of nodes you wish the cluster to have.
-  - **Machine type** - The machine type of the Virtual Machine instance that
-    the cluster will be based on. Read more about [the available machine types](https://cloud.google.com/compute/docs/machine-types).
-  - **Project namespace** - The unique namespace for this project. By default you
-    don't have to fill it in; by leaving it blank, GitLab will create one for you.
-1. Click the **Create cluster** button.
+1. Navigate to your project's **CI/CD > Cluster** page
+1. If you want to let GitLab create a cluster on GKE for you, go through the
+   following steps, otherwise skip to the next one.
+    1. Click on **Create with GKE**
+    1. Connect your Google account if you haven't done already by clicking the
+       **Sign in with Google** button
+    1. Fill in the requested values:
+      - **Cluster name** (required) - The name you wish to give the cluster.
+      - **GCP project ID** (required) - The ID of the project you created in your GCP
+        console that will host the Kubernetes cluster. This must **not** be confused
+        with the project name. Learn more about [Google Cloud Platform projects](https://cloud.google.com/resource-manager/docs/creating-managing-projects).
+      - **Zone** - The zone under which the cluster will be created. Read more about
+        [the available zones](https://cloud.google.com/compute/docs/regions-zones/).
+      - **Number of nodes** - The number of nodes you wish the cluster to have.
+      - **Machine type** - The machine type of the Virtual Machine instance that
+        the cluster will be based on. Read more about [the available machine types](https://cloud.google.com/compute/docs/machine-types).
+      - **Project namespace** - The unique namespace for this project. By default you
+        don't have to fill it in; by leaving it blank, GitLab will create one for you.
+1. If you want to use your own Kubernetes cluster, click on
+   **Add an existing cluster** and fill in the details as described in the
+   [Kubernetes integration](../integrations/kubernetes.md) documentation.
+1. Finally, click the **Create cluster** button
 
 After a few moments, your cluster should be created. If something goes wrong,
 you will be notified.