Clarify K8s service CIDR selection when using hybrid nodes

[csplinter]

For hybrid nodes customers, the remote node and pod CIDRs can't conflict with the Kubernetes service CIDR. The default K8s service CIDR for EKS is 172.16.0.0/16 - we should state that in the hybrid nodes docs. We also need to clarify how the K8s service CIDR default is selected and whether a different CIDR is selected if you supply 172.16.0.0/16 for your remote node or pod CIDRs.