old_contents: import React from 'react'
  import ReactDOM from 'react-dom'
  import App from './components/app'
  import './css/bootstrap.css'
  import './css/index.css'
  import registerServiceWorker from './registerServiceWorker'
  
  ReactDOM.render(
    <App />,
    document.getElementById('root')
  )
  registerServiceWorker()
new_contents: import React from 'react'
  import ReactDOM from 'react-dom'
  import { BrowserRouter as Router, Route } from 'react-router-dom'
  import App from './components/app'
  import './css/bootstrap.css'
  import './css/index.css'
  import registerServiceWorker from './registerServiceWorker'
  
  ReactDOM.render(
    <Router>
      <Route path='/' component={App} />
    </Router>,
    document.getElementById('root')
  )
  registerServiceWorker()
subject: Set up react-router