Minor modifications to the README

Author: dmadeka

README.md

@@ -1,7 +1,9 @@
 bqplot
 ======
 
-bqplot is a plotting system for the Jupyter notebook.
+bqplot is a Grammar of Graphics based interactive plotting framework for the Jupyter notebook.
+
+![bqplot](./bqplot-screencast.gif)
 
 Goals
 -----
@@ -122,6 +124,8 @@ Help / Documentation
 
 - API reference documentation: [![Read the documentation of the stable version](https://readthedocs.org/projects/pip/badge/?version=stable)](http://bqplot.readthedocs.org/en/stable/) [![Read the documentation of the development version](https://readthedocs.org/projects/pip/badge/?version=latest)](http://bqplot.readthedocs.org/en/latest/)
 
+- [![Join the chat at https://gitter.im/bloomberg/bqplot](https://badges.gitter.im/Join%20Chat.svg)](https://gitter.im/bloomberg/bqplot?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge&utm_content=badge)
+
 License
 -------