Rails and React Server Side Rendering, with Webpacker and Hypernova

Hey all, I realise that neither Webpacker nor Hypernova are brand spanking new tools, but when I went to find a "getting started" tutorial, I found nothing up to date. Even the official Hypernova docs are written for Rails ~3.2 era and don't explain how to set up your JS build to support client + server side rendering. So hopefully this tutorial is helpful to someone else too!