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.

首先定位文档网站的 webpack 配置，并检查它是否暴露了 Gatsby 风格的 plugin hook。将 `@expo/webpack-config/addons` 中提议的 `withUnimodules` wrapper 与链接的 gatsby-plugin-react-native-web 集成进行比较。当 Paper 和 Reanimated 的 web component 演示可以直接嵌入文档并进行试用时，即视为完成。

由索引模型根据 Issue 内容生成。