Merge pull request kubernetes#3197 from elmiko/update-capi-readme

add CAPI prerequisites section to cluster-autoscaler README

Author: k8s-ci-robot

cluster-autoscaler/cloudprovider/clusterapi/README.md

@@ -10,6 +10,14 @@ cluster.
 The cluster-api provider requires Kubernetes v1.16 or greater to run the
 v1alpha3 version of the API.
 
+## Cluster API Prerequisites
+
+Please be aware that currently the cluster autoscaler only supports CAPI
+clusters that have joined their management and workload clusters into a single
+cluster. For more information about this please see the
+[Cluster API Concepts documentations](https://cluster-api.sigs.k8s.io/user/concepts.html)
+and the [`clusterctl move` command documentaion](https://cluster-api.sigs.k8s.io/user/concepts.html).
+
 ## Starting the Autoscaler
 
 To enable the Cluster API provider, you must first specify it in the command