title: The relation between "docker/swarm" and "docker/swarmkit"
body: <p>I am already familiar with <a href="https://github.com/docker/swarm" rel="noreferrer">docker/swarm</a>, but find there occurs a "new" project: <a href="https://github.com/docker/swarmkit" rel="noreferrer">docker/swarmkit</a>. But unfortunately, after reading the <a href="https://github.com/docker/swarmkit/blob/master/README.md" rel="noreferrer">README</a>, I still can't figure out what is the function of <code>docker/swarmkit</code>. Could anyoone help to elaborate the relations between <code>docker/swarm</code> and <code>docker/swarmkit</code>? Why is <code>docker/swarmkit</code> born?</p>