Add support info (#272)

README.md

@@ -4,6 +4,11 @@ This action configures authentication to a [GKE cluster][gke] via a `kubeconfig`
 
 Authentication is performed by generating a [short-lived token][token] (default behaviour) or via the [GCP auth plugin][gcp-auth-plugin] present in `kubectl` which uses the service account keyfile path in [GOOGLE_APPLICATION_CREDENTIALS][gcp-gcloud-auth].
 
+**This is not an officially supported Google product, and it is not covered by a
+Google Cloud support contract. To report bugs or request features in a Google
+Cloud product, please contact [Google Cloud
+support](https://cloud.google.com/support).**
+
 ## Prerequisites
 
 This action requires: