Add React 18 Streaming docs

Author of [vite-plugin-ssr](https://vite-plugin-ssr.com/) here; some of my users are trying to use Relay with React 18 Suspended Streams but there seem to be no official recommendations/docs about Relay + React 18.

It would greatly help the community to add docs or examples about how to use Relay with React 18, especially in the context of SSR + Suspense + Streaming.

Happy to contribute a Vite + vite-plugin-ssr + Relay example.

No files or tests are named. Review the existing Relay documentation and examples for React 18, SSR, Suspense, and streaming, then investigate the proposed Vite + vite-plugin-ssr setup. Done means documenting clear recommendations or adding a working example for Relay with React 18 streaming.

Written by the indexing model from the issue text.