update prereq

Author: kaitlynmichael

content/operate/kubernetes/deployment/helm.md

@@ -17,7 +17,8 @@ Helm charts provide a simple way to install the Redis Enterprise for Kubernetes
 - A [supported distribution]({{< relref "/operate/kubernetes/reference/supported_k8s_distributions" >}}) of Kubernetes.
 - At least three worker nodes.
 - [Kubernetes client (kubectl)](https://kubernetes.io/docs/tasks/tools/).
-- [Helm 3.10 or later](https://helm.sh/docs/intro/install/).
+- [Helm 3.10 or later](https://helm.sh/docs/intro/install/)
+    or 3.18 for migrating from a non-Helm installation.
 
 ### Example values