document css file loading

[martindemello]

It took me a good bit of googling and trial and error to discover that if I installed primer-css via npm, the way to get it into my rails app was by adding

import '@primer/css/dist/primer.css'

in app/frontend/entrypoints/application.js (rather than e.g. in application.css or via a stylesheet tag in my erb file)

An overview page on the various ways to install and include third-party css libraries into a vite/rails setup would have been very helpful.

[ElMassimo]

Given how many CSS libraries are available on npm, it would be quite a large section (and might go out of date quickly).

Perhaps it would be better to suggest a change in the docs for primer-css, which already cover this?