Added description to README

===NOT READY TO MERGE==

Given the email thread by @bensheldon on better documentation, since I was already taking a look at this repo, I figured I'd take a quick stab at improving the README.

Still a work in progress but opening up this pull request now, more as a way to get feedback and perhaps spark some conversation.

A preview of the markdown rendered, can be seen on my fork of repo:
https://github.com/tinio/public_art_finder/tree/doc

@mertonium thoughts?