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
```

We can have an image with the command line included but it won't work that well as kubecfg often reads from local files.

We also shouldn't assume that our users are golang users or even have golang installed.  Instead, we should assume that most users can/will/should download our tarball release (we can slim it down eventually to not include the server tars).  That tarball release has pre-compiled kubecfg/kubectl binaries.