document docker cgroupdriver req (kubernetes#5937)

docs/setup/independent/install-kubeadm.md

@@ -125,6 +125,20 @@ systemctl enable docker && systemctl start docker
 
 {% endcapture %}
 
+**Note**: Make sure that the cgroup driver used by kubelet is the same as the one used by 
+Docker. To ensure compatability you can either update Docker, like so:
+
+```bash
+cat << EOF > /etc/docker/daemon.json
+{
+  "exec-opts": ["native.cgroupdriver=systemd"]
+}
+EOF
+```
+
+and restart Docker. Or ensure the `--cgroup-driver` kubelet flag is set to the same value 
+as Docker (e.g. `cgroupfs`).
+
 {% assign tab_set_name = "docker_install" %}
 {% assign tab_names = "Ubuntu, Debian or HypriotOS;CentOS, RHEL or Fedora" | split: ';' | compact %}
 {% assign tab_contents = site.emptyArray | push: docker_ubuntu | push: docker_centos %}