You can either install globally or locally.
electron-react-tools start in your app directry.
Install as a dev dependency
npm install --dev electron-react-tools
yarn add --dev electron-react-tools
"electron-start": "electron-react-tools start" line to scripts in package.json file. Then run
npm run electron-start
This version assumes your application's entry point is ./src/index.js and ./public/index.html
In further versions these will be configurable.