react-native-vector-icons is missing

The library is using `react-native-vector-icons`. But it's not mentioned in the document. So, if anyone who are not using `react-native-vector-icons` will facing the error below:

```
The development server returned response error code: 500

URL: http://10.0.3.2:8081/index.android.bundle?platform=android&dev=true&hot=false&minify=false

Body:
{"from":"/Users/giang.nguyen/Development/practice/Todo/node_modules/react-native-mdcore/src/components/Icon.js","to":"react-native-vector-icons","message":"Unable to resolve module `react-native-vector-icons` from `/Users/giang.nguyen/Development/practice/Todo/node_modules/react-native-mdcore/src/components/Icon.js`:
```