docker: add cluster bootstrap and doc

This bootstrap a local kubernetes cluster by running the `kubelet` as a bare`docker` container, and passing it a pod manifest with the cluster components.

Changes:
- add getting started guide for `docker` locally
- modify `build/` to allow boot2docker on all platform
- add `kubernetes-bootstrap` image
- embed cluster-pod manifest in bootstrap image

You should be able to try this at home with:
```
docker run -d -p 10250:10250 -v /var/run/docker.sock:/var/run/docker.sock proppy/kubestrap
export KUBERNETES_MASTER=$DOCKER_HOST_IP:8080
kubecfg list pods
kubecfg -p 8181:80 run nginx 1 kube-nginx
curl $DOCKER_HOST_IP:8181
```

Can you put a little more of an explanation here?  We have the Vagrant set up and the "local not in container" script.

Something like:

> This method runs a local kubernetes cluster self hosted in Docker itself.  The Kubelet is started in a container with access to the Docker API.  It then launches a pod of containers that comprise the rest of a local-only kubernetes cluster.