added a section about that the Knative variant runs on top of OpenShi…

…ft or Kubernetes and requires a Knative installation

README.md

@@ -104,6 +104,9 @@ Pre-built images for all of the applications in the system can be found at [`qua
 
 Deployment descriptors for these images are provided in the [`deploy/k8s`](deploy/k8s) directory. There are versions for [OpenShift](https://www.openshift.com), [Minikube](https://quarkus.io/guides/deploying-to-kubernetes#deploying-to-minikube), [Kubernetes](https://www.kubernetes.io), and [Knative](https://knative.dev).
 
+> [!NOTE]
+> The [Knative](https://knative.dev/docs/) variant can be used on any Knative installation that runs on top of Kubernetes or OpenShift. For OpenShift, you need "OpenShift Serverless" installed from the OpenShift operator catalog. Using Knative has the benefit that services are scaled down to zero replicas when they are not used.
+
 The only real difference between the Minikube and Kubernetes descriptors is that all the application `Service`s in the Minikube descriptors use `type: NodePort` so that a list of all the applications can be obtained simply by running `minikube service list`.
 
 > [!NOTE]