Include overview in the README

[claforte]

Right now the README only includes a quote from Tolkien, so when we point others to this project, many people probably give up instead of taking a serious look. I recommend you start with a brief overview, e.g. cut-and-paste the intro from the docs:

[vchuravy]

I would like to direct people as quickly as possible to the docs, but you are of course right there is no elevator pitch, but just a table of CI being wonky.

PRs are welcome ;)