added info in the readme

README.md

@@ -7,4 +7,13 @@
 [![Packagist Version](https://img.shields.io/packagist/v/remi-san/specification.svg?style=flat-square)](https://packagist.org/packages/remi-san/specification)
 [![Coverage Status](https://img.shields.io/scrutinizer/coverage/g/remi-san/specification.svg?style=flat-square)](https://scrutinizer-ci.com/g/remi-san/specification/code-structure)
 
-A lib to use the specification pattern
+A lib to ease the use the **specification pattern**.
+
+Your specification classes can extend the `AbstractSpecification` class which already implement
+the following methods from the `Specification` interface:
+ - `andSatisfies`
+ - `orSatisfies`
+ - `not`
+
+ You'll have to implement the `isSatisfiedBy` method to add the domain logic.
+