Support RNW

Hey

As this project is used for both Paper and Reanimated (both supporting web platform), it would be cool if we could embed web component demos directly in the doc.

Is there a way to customize webpack currently, like a gatsby plugin or something?

Wrapping the webpack config with `withUnimodules` from `import { withUnimodules } from '@expo/webpack-config/addons'` should do the job, see https://github.com/slorber/gatsby-plugin-react-native-web/blob/master/src/gatsby-node.js

That could be a better experience and also a "proof" that web support is good in those libs if user was able to try web support easily.

Inizia individuando la configurazione webpack del sito della documentazione e verificando se espone un plugin hook in stile Gatsby. Confronta il wrapper `withUnimodules` proposto di `@expo/webpack-config/addons` con l'integrazione gatsby-plugin-react-native-web collegata. Il lavoro è completato quando le demo di componenti web per Paper e Reanimated possono essere incorporate e provate direttamente nella documentazione.

Scritto dal modello di indicizzazione a partire dal testo della issue.