add jsDelivr CDN & reformat README Installation

I've set up [automated jsDelivr CDN hosting](https://github.com/jsdelivr/jsdelivr/tree/master/files/interact.js) for you.  All you need to do is make a new GitHub 'release', the PR-bot & approval should happen in minutes to hours.

I hope you don't mind the reformatting; 4 'or's are too many IMHO :)