Add docs for kops, explain when kops and when kubeadm

Quick getting started guide for kops.

Also try to provide some guidance as to when to use kops and when
kubeadm; based on discussions with sig-cluster-lifecycle that kubeadm is
a building block and not a provisioning tool.

I used "kubeadm" as a simplifying concept for "kubeadm and the other
work done by sig-cluster-lifecycle that kubeadm is a part of", in that
tools that don't (yet) use kubeadm are still leveraging the kubeadm
stream of work.

_data/guides.yml

@@ -10,6 +10,8 @@ toc:
     path: /docs/whatisk8s/
   - title: Installing Kubernetes on Linux with kubeadm
     path: /docs/getting-started-guides/kubeadm/
+  - title: Installing Kubernetes on AWS with kops
+    path: /docs/getting-started-guides/kops/
   - title: Hello World on Google Container Engine
     path: /docs/hellonode/
   - title: Downloading or Building Kubernetes