Merge pull request #9 from williamboman/docs/example-gif-readme

readme: add demo gif

Author: jakezatecky

README.md

@@ -5,7 +5,10 @@
 [![devDependency Status](https://david-dm.org/jakezatecky/react-checkbox-tree/dev-status.svg?style=flat-square)](https://david-dm.org/jakezatecky/react-checkbox-tree#info=devDependencies)
 [![GitHub license](https://img.shields.io/badge/license-MIT-blue.svg?style=flat-square)](https://raw.githubusercontent.com/jakezatecky/react-checkbox-tree/master/LICENSE.txt)
 
-Checkbox treeview for React.
+> Checkbox treeview for React.
+
+![Demo](demo.gif)
+
 
 # Usage