Add vite details to docs

[madroneropaulo]

I spent quite some time trying to figure out why my vite project was not working when I did everything per this guide.
https://docs.farcaster.xyz/auth-kit/installation
this should include instructions to install vite node polyfills
"vite-plugin-node-polyfills": "^0.21.0"
And configure it in vite.config.ts
plugins: [react(), nodePolyfills({ include: ["buffer"] })],
Sorry for not contributing with a PR, but I think the person in charge of docs can change this way faster than me.