update README

Author: sugyan

README.md

@@ -1 +1,6 @@
-# docker-heroku-python-opencv
+# Python Docker Image with OpenCV 3.0
+
+This repository contains a Python and OpenCV docker image, for use with [Heroku](http://heroku.com) and the
+[heroku-docker](https://github.com/heroku/heroku-docker) CLI plugin.
+
+[Image available on Dockerhub](https://hub.docker.com/r/sugyan/heroku-python-opencv/).