Update install-kubeadm.md

Propose adding config reference to load br_netfilter at boot up to prevent issues with the module not being loaded after reboot.

content/en/docs/setup/production-environment/tools/kubeadm/install-kubeadm.md

@@ -59,6 +59,10 @@ Make sure that the `br_netfilter` module is loaded. This can be done by running
 As a requirement for your Linux Node's iptables to correctly see bridged traffic, you should ensure `net.bridge.bridge-nf-call-iptables` is set to 1 in your `sysctl` config, e.g.
 
 ```bash
+cat <<EOF | sudo tee /etc/modules-load.d/k8s.conf
+br_netfilter
+EOF
+
 cat <<EOF | sudo tee /etc/sysctl.d/k8s.conf
 net.bridge.bridge-nf-call-ip6tables = 1
 net.bridge.bridge-nf-call-iptables = 1