docs(dashd): include required 'services' option

[coolaj86]

I'm not sure if this is the most up-to-date preferred style.

This example https://github.com/dashevo/dashcore-node/blob/master/regtest/cluster.js seems to suggest that it would be just as well, or perhaps better, to nest the config for the service in the services array:

{
  "services": [
    "name": "dashd",
    "config": {
      "connect": [ /*...*/ ],
    }
  ]
}

This seems to suggest that serviceConfig is deprecated?

[shumkov]

👍