readme.md: very simple readme with example links [Closes #9]

Author: Matej Humpal

readme.md

@@ -3,3 +3,7 @@ Nette PHP Generator
 
 [![Downloads this Month](https://img.shields.io/packagist/dm/nette/php-generator.svg)](https://packagist.org/packages/nette/php-generator)
 [![Build Status](https://travis-ci.org/nette/php-generator.svg?branch=master)](https://travis-ci.org/nette/php-generator)
+
+Generate PHP code with a simple programmatical API.
+
+[Sample PHP code definition](https://github.com/nette/php-generator/blob/master/tests/PhpGenerator/ClassType.phpt) → [sample output](https://github.com/nette/php-generator/blob/master/tests/PhpGenerator/ClassType.expect) with magic ```__toString()``` method.