newbie guidance: indicate where to place new assets so that the webpack process adopts them

For those unfamiliar with the magic of webpack and webpack-dev-server, include a brief paragraph on where to store new assets (like a materialize.css) in the project structure so that page processing pipeline will adopt and inject those new assets into app-specific views.

I thought @imports in the app's index.css might do the trick but, out of the box, that file isn't processed.