Renamed the file to be README.md instead of readme.md - the uppercase name is traditionally used, since it brings the file higher up the alphabetically-sorted directory view on a case-sensitive system.

Other than that, this file appears completely new as, per the commit message, it fully embraces Markdown, instead of sticking to the WP plugin readme.txt file format, since you'd included a note that this plugin wasn't allowed to be included on there.

Sticking to the right header levels (starting off with a `#`, then `##`) is also more semantically correct once it's converted to HTML.