Update the supported version of Kubernetes to 1.12. (googleforgames#967)

site/content/en/docs/Installation/_index.md

@@ -23,6 +23,7 @@ In this quickstart, we will create a Kubernetes cluster, and populate it with th
 
 ## Usage Requirements
 
+{{% feature expiryVersion="0.12.0" %}}
 - Kubernetes cluster version 1.11
     - [Minikube](https://github.com/kubernetes/minikube), [Kind](https://github.com/kubernetes-sigs/kind), [Google Kubernetes Engine](https://cloud.google.com/kubernetes-engine/),
       [Azure Kubernetes Service](https://azure.microsoft.com/en-us/services/kubernetes-service/) and [Amazon EKS](https://aws.amazon.com/eks/) have been tested
@@ -38,6 +39,24 @@ In this quickstart, we will create a Kubernetes cluster, and populate it with th
 > Later versions of Kubernetes may work, but this project is tested against 1.11, and is therefore the supported version.
 > Agones will update its support to n-1 version of what is available across all major cloud providers - GKE, EKS and AKS
 
+{{% /feature %}}
+{{% feature publishVersion="0.12.0" %}}
+- Kubernetes cluster version 1.12
+    - [Minikube](https://github.com/kubernetes/minikube), [Kind](https://github.com/kubernetes-sigs/kind), [Google Kubernetes Engine](https://cloud.google.com/kubernetes-engine/),
+      [Azure Kubernetes Service](https://azure.microsoft.com/en-us/services/kubernetes-service/) and [Amazon EKS](https://aws.amazon.com/eks/) have been tested
+    - If you are creating and managing your own Kubernetes cluster, the
+    [MutatingAdmissionWebhook](https://kubernetes.io/docs/admin/admission-controllers/#mutatingadmissionwebhook-beta-in-19), and
+    [ValidatingAdmissionWebhook](https://kubernetes.io/docs/admin/admission-controllers/#validatingadmissionwebhook-alpha-in-18-beta-in-19)
+    admission controllers are required.
+    We also recommend following the
+    [recommended set of admission controllers](https://kubernetes.io/docs/admin/admission-controllers/#is-there-a-recommended-set-of-admission-controllers-to-use).
+- Firewall access for the range of ports that Game Servers can be connected to in the cluster.
+- Game Servers must have the [game server SDK]({{< ref "/docs/Guides/Client SDKs/_index.md"  >}}) integrated, to manage Game Server state, health checking, etc.
+
+> Later versions of Kubernetes may work, but this project is tested against 1.12, and is therefore the supported version.
+> Agones will update its support to n-1 version of what is available across all major cloud providers - GKE, EKS and AKS
+{{% /feature %}}
+
 ## Setting up a Google Kubernetes Engine (GKE) cluster
 
 Follow these steps to create a cluster and install Agones directly on Google Kubernetes Engine (GKE).