Fix API docs - should be settings.confg

[lholmquist]

The API docs are not totally correct. For example, if a user needs to pass in some custom config values, if they were to look at the docs, it looks like this should be passed in:

  { key1: value, key2: value }

when it should be

  {
    config: { key1: value, key2: value }
  }

The readme is correct, this is a simple API doc fix