In this project a dummy TabNavigator is displayed as main screen, the default tab contains buttons to navigate to the others, to change theme (needs to reload) and to delete all the data saved in local storage, the other tabs are the smart shopping list and the recipe suggestion. That TabNavigator will be replaced by the one in the main Alfred app, to do so it simply needs to take both the screens and plug them in that navigator, maybe adjusting the styles to suit globally in the app (can be done in StyleSheet.js and ColorSets.js). To know more about the code just look on it, every class and method is carefully explained with comments.
The most recent version of the create-react-native-app guide is available here.