React.js: Añadir Bootstrap

Seguir los pasos de:
https://react-bootstrap.github.io/getting-started/introduction

Básicamente es:
Instalar:
npm install react-bootstrap bootstrap

En index.js:
import 'bootstrap/dist/css/bootstrap.min.css';

En el head de index.html:
<script src="https://unpkg.com/react/umd/react.production.min.js" crossorigin></script>
<script
  src="https://unpkg.com/react-dom/umd/react-dom.production.min.js"
  crossorigin></script>
<script
  src="https://unpkg.com/react-bootstrap@next/dist/react-bootstrap.min.js"
  crossorigin></script>
<script>var Alert = ReactBootstrap.Alert;</script>