adding Docker instructions to the backend;

Author: Bruno Krebs

backend/.dockerignore

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+node_modules
+npm-debug.log

backend/Dockerfile

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+# reference: https://nodejs.org/en/docs/guides/nodejs-docker-webapp/
+FROM node:10.13
+
+# Create app directory
+WORKDIR /usr/src/app
+
+# Install app dependencies
+# A wildcard is used to ensure both package.json AND package-lock.json are copied
+# where available (npm@5+)
+COPY package*.json ./
+
+RUN npm install
+# If you are building your code for production
+# RUN npm install --only=production
+
+# Bundle app source
+COPY . .
+
+EXPOSE 8081
+CMD [ "node", "src" ]

backend/README.md

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+# React Tutorial
+
+[Auth0] has developed this application to support [the React Tutorial published here](https://auth0.com/blog/react-tutorial-building-and-securing-your-first-app/). Head to the article to learn about how everything works.
+
+## Running the Application
+
+The easiest way to run this application is to issue `node src` from a terminal pointing to this directory. This command, as you may know, requires Node.js and NPM installed locally. If you don't have those, [you can install them in a few minutes](https://nodejs.org/en/download/).
+
+Another alternative is to use Docker to run the app in a container. To do so, you can issue the following commands:
+
+```bash
+docker build -t react-tutorial-backend .
+
+docker run --name react-tutorial-backend -d -p 8081:8081 react-tutorial-backend
+```
+
+This will make your API accessible on the following URL: [`http://localhost:8081`].
+
+## Releasing a new Docker Image
+
+Make sure you are currently logged into Docker and then issue the following commands:
+
+```bash
+docker build -t brunokrebs/react-tutorial-backend .
+
+docker push brunokrebs/react-tutorial-backend
+```
+
+In the code snippet above, you will need to replace `brunokrebs` with your own Docker username (unless you are me 😊).
+
+If you do push a Docker image to [Docker Hub](https://hub.docker.com/), then you can use it like this:
+
+```bash
+docker run --name react-tutorial-backend -d -p 8081:8081 brunokrebs/react-tutorial-backend
+```