Add BunJs command and installation guide

[imran-khani]

Goals

1. user can download next-auth with bun
2. bun install like command like npm install
3. cause bun is fast for me

Non-Goals

Background

I found at many sites that they have updated the commands guide on their site with the arrival of bun js 1.0. I was wondering to suggest this feature to next-auth owners.

Proposal

This can be added to site installation guide on how to install this app with bun.