Docker image for building a React Native app on CircleCI

1. docker login and log-in with an user belonging to the getmoona organization on Docker Hub
2. Edit the file Dockerfile
3. docker build -t getmoona/react-native-circleci .
4. docker push getmoona/react-native-circleci

Web interface: https://hub.docker.com/r/getmoona/react-native-circleci/