README: add gif showcase

README.md

@@ -5,6 +5,8 @@ Rector is under development phase in 2018, to figure out the best way to use it
 [![Build Status](https://img.shields.io/travis/rectorphp/rector/master.svg?style=flat-square)](https://travis-ci.org/rectorphp/rector)
 [![Coverage Status](https://img.shields.io/coveralls/RectorPHP/Rector/master.svg?style=flat-square)](https://coveralls.io/github/rectorphp/rector?branch=master)
 
+![Rector-showcase](docs/images/rector-showcase.gif)
+
 Rector **upgrades your application** for you, with focus on open-source projects:
 
 <p align="center">
@@ -19,6 +21,7 @@ Rector **upgrades your application** for you, with focus on open-source projects
     <a href="/src/config/level/twig"><img src="/docs/images/twig.png"></a>
 </p>
 
+
 Rector can:
 
 - [Rename classes](#replace-a-class-name)