message: Website: fix links in react section (##1265)
  broken link to demo source code
  change link+name of react-sigma
diff: <h3>Can I use sigma.js in my <a href="https://reactjs.org/">React</a> application?</h3>
  <p>
  Yes, the best way is certainly to use the
  - <a href="https://github.com/sim51/react-sigma-v2">react-sigma-v2</a>. The example on top of this page is
  + <a href="https://github.com/sim51/react-sigma">@react-sigma</a>. The example on top of this page is
  developed using it, you can check the
  - <a href="https://github.com/jacomyal/sigma.js/tree/main/examples/website-showcase">sourcecode</a> to get
  + <a href="https://github.com/jacomyal/sigma.js/tree/main/demo">sourcecode</a> to get
  an idea.
  </p>
  </li>
  