Define the "why" in the README

[eddelbuettel]

So now that @eitsupi cleaned up and simplified and this works on top of his work already bringing bspm (thanks, @Enchufa2, all weirdnesses experienced here in prior version were local) the README.md needs two or three trenchant bullet points of why people should start here and with this.

Obviously, being able to run any CRAN package near-immediately on a cloud-hosted box is great. Maybe we can record a quick screen shot video to post your example.R in action. (Sadly, peek which I used before seems to have some sort of measles under 23.04. If needed I could try on a 22.04 machine.)