11a6aeaea3
Added JS topic guides and also updated the existing Swift/JS ones a bit. I didn't add a guide for remote settings, since I don't think we want to encourage users to use this one over the official client. Split up the notes at the begining into prerequites and notes on async. My hope is that the async notes can go away once we start making our components async. Differential Revision: https://phabricator.services.mozilla.com/D228481