[Doc] Use startup taint for better cluster-autoscaler behaviour

[b4nst]

I think it would be beneficial for user to replace the taint example (kubeip.com/not-ready) by a startup taint (startup-taint.cluster-autoscaler.kubernetes.io/kubeip-not-ready or equivalent). This would avoid a chicken and egg scheduling issue, as startup taint are ignored by cluster-autoscaler.