Add rtype interface for initialFeatures to Readme.

[kennylavender]

For #16.

I am unsure how to describe initialFeatures in rtype, so I am experimenting here.

// example object
const initialFeatures = {
  'comments': {
    enabled: false,
    dependencies: []
  },
  'user-ratings': {
    enabled: false,
    dependencies: ['comments']
  }
}

interface Feature {
  enabled: Boolean,
  dependencies: Array
}
interface IntialFeatures {
  [featureName: String]: Feature
}

[kennylavender]

I think I have the above signatures correct, they feel a bit odd to me though. I think they feel odd because the Feature interface does not have a name, and the rest of the properties are useless without a name.

I wonder if we should make the signatures and implementation more intuitive with something like

const initialFeatures = [{
    name: 'comments',
    enabled: false,
    dependencies: []
  },{
    name: 'user-ratings',
    enabled: false,
    dependencies: ['comments']
  }];

interface Feature {
  name: String,
  enabled?: false,
  dependencies?: [...featureName: String]
}
const initialFeatures = [ ...Feature]

[kennylavender]

@ericelliott @thoragio thoughts?

[thoragio]

I think the second way is clearer, and it also addresses my array or object question by using an array to hold the list of features, which is more intuitive IMO.

[kennylavender]

@thoragio cool thanks, I think I might make a pr that changes the implementation to this