Have a static version of our home page for better SEO

At build time we should generate a static version of our home page so that the landing page is faster and search engines are more happily indexing our content.

One way could be to use https://reactjs.org/docs/react-dom-server.html in a custom script.
But there may be better options. For example [next.js](https://github.com/zeit/next.js)? (it may be too big for us, I really don't know).

┆Issue is synchronized with this [Jira Task](https://mozilla-hub.atlassian.net/browse/FP-47)