Add more reading material for frontend engineers
Created by: felixfbecker
Added a few more links that I think every frontend hire would benefit from reading (or at least skimming, or being aware it exists :)) before working on a big PR.
I specifically wrote these in a way that they each have a little explainer what value the reader will get from reading it, and being open about which ones should be read thoroughly, and which others are okay to just be skimmed.