Changes

===compose && swarm common part===

* '''command''': Override the default command. <pre> command: ["bundle", "exec", "thin", "-p", "3000"] </pre>

Links also express dependency between services in the same way as depends_on, so they determine the order of service startup.

<span style="color: red>Note: If you define both links and networks, services with links between them must share at least one network in common in order to communicate.</span>

=== swarm only===