Request: Add prebuilt versions to github releases

[alok]

This is just a nice-to-have (pandoc isn't that hard to install), but I'd certainly appreciate being able to just download a mostly up-to-date version of the book by going to this repo.

[dr-manhattan]

It's not easy to install if you're not on linux and even then my attempt threw an obscure error on the last step. So ++1

[bob-carpenter]

RStudio has everything preinstalled, I think.

If someone could create a PR to add a shell script or makefile that'll build an HTML version in the right way to launch on GitHub pages, that'd be super helpful. I don't really have the time or inclination to figure out how to do it until the book gets further along and I'm actively soliciting feedback.