update README with multi-master notes
update README with multi-master notes

kubernetes-sigs/kubespray,sgm-media/kargo,Lendico/kargo,kubernetes-sigs/kubespray,galthaus/setup-kubernetes,Abdelsalam-Abbas/kubespray_fork,hatch-k8s/kargo,galthaus/setup-kubernetes,Smana/setup-kubernetes,kubernetes-sigs/kubespray,VincentS/kargo,Atoms/kubespray,Atoms/kubespray,kubernetes-incubator/kubespray,Abdelsalam-Abbas/kubespray_fork,kubespray/kargo,rogerwelin/kargo,ayaz/kubespray,hatch-k8s/kargo,sgm-media/kargo,rogerwelin/kargo,VincentS/kargo,Atoms/kubespray,kubernetes-incubator/kargo,Atoms/kubespray,insequent/kargo,jcsirot/kubespray,kubernetes-sigs/kubespray,Smana/setup-kubernetes,kubernetes-incubator/kargo,Lendico/kargo,jonbec/kargo,kubernetes-incubator/kubespray,insequent/kargo,jcsirot/kubespray,jonbec/kargo,kubespray/kargo,ayaz/kubespray