Add instructions for overriding autodetected network interface.

docs/getting-started-guides/kubeadm.md

@@ -42,16 +42,6 @@ You will install the following packages on all the machines:
 
 For each host in turn:
 
-<!--
-    # curl https://packages.cloud.google.com/apt/doc/apt-key.gpg | apt-key add -
-    # cat <<EOF > /etc/apt/sources.list.d/kubernetes.list
-    deb http://packages.cloud.google.com/apt kubernetes-xenial main
-    EOF
-    # apt-get update
-    # apt-get install -y kubeadm docker.io§
--->
-
-
 * SSH into the machine and become `root` if you are not already (for example, run `sudo su -`).
 * If the machine is running Ubuntu 16.04, run:
 
@@ -92,6 +82,9 @@ To initialize the master, pick one of the machines you previously installed `kub
 
      # kubeadm init
 
+**Note:** this will autodetect the network interface to advertise the master on as the interface with the default gateway.
+If you want to use a different interface, specify `--api-advertise-addresses=<ip-address>` argument to `kubeadm init`.
+
 This will download and install the cluster database and "control plane" components.
 This may take several minutes.