Mention alternate architectures for RPMs in kubeadm doc.

Now that we have new repositories to house RPMs for other architectures,
and are populating them with new releases, we should advertise them in
the kubeadm getting started instructions.

docs/getting-started-guides/kubeadm.md

@@ -116,10 +116,11 @@ For each host in turn:
 * If the machine is running CentOS, run:
 
   ``` bash
+  ARCH=x86_64
   cat <<EOF > /etc/yum.repos.d/kubernetes.repo
   [kubernetes]
   name=Kubernetes
-  baseurl=https://packages.cloud.google.com/yum/repos/kubernetes-el7-x86_64
+  baseurl=https://packages.cloud.google.com/yum/repos/kubernetes-el7-${ARCH}
   enabled=1
   gpgcheck=1
   repo_gpgcheck=1
@@ -132,6 +133,10 @@ For each host in turn:
   systemctl enable kubelet && systemctl start kubelet
   ```
 
+  If your hosts are a different architecture, you will need to modify the
+  `ARCH=x86_64` line above to the correct value. RPMs are currently available
+  for `armhfp`, `aarch64`, `ppc64le`, `s390x`, and `x86_64`.
+
   The kubelet is now restarting every few seconds, as it waits in a crashloop for
   kubeadm to tell it what to do.
 
@@ -470,13 +475,10 @@ control of your Kubernetes cluster.
 
 ## kubeadm is multi-platform {#multi-platform}
 
-kubeadm deb packages and binaries are built for amd64, arm and arm64, following
-the [multi-platform
+kubeadm deb/rpm packages and binaries are built for amd64, arm64, armhfp,
+ppc64el, and s390x following the [multi-platform
 proposal](https://github.com/kubernetes/kubernetes/blob/master/docs/proposals/multi-platform.md).
 
-deb-packages are released for ARM and ARM 64-bit, but not RPMs (yet, reach out
-if there's interest).
-
 Currently, only the pod networks flannel and Weave Net work on multiple architectures.
 For Weave Net just use its [standard install](https://www.weave.works/docs/net/latest/kube-addon/).