Link Board Backend

Tutorials I've followed

• https://medium.freecodecamp.org/how-to-enable-es6-and-beyond-syntax-with-node-and-express-68d3e11fe1ab
• https://medium.com/@sgroff04/configure-eslint-prettier-and-flow-in-vs-code-for-react-development-c9d95db07213 (configuring eslint + flow)