Added packagist version badge to README.md

Author: creocoder

README.md

@@ -2,6 +2,7 @@
 
 [![Build Status](https://img.shields.io/travis/creocoder/yii2-nested-sets/master.svg?style=flat-square)](https://travis-ci.org/creocoder/yii2-nested-sets)
 [![Code Coverage](https://img.shields.io/scrutinizer/coverage/g/creocoder/yii2-nested-sets/master.svg?style=flat-square)](https://scrutinizer-ci.com/g/creocoder/yii2-nested-sets/?branch=master)
+[![Packagist Version](https://img.shields.io/packagist/v/creocoder/yii2-nested-sets.svg?style=flat-square)](https://packagist.org/packages/creocoder/yii2-nested-sets)
 
 A modern nested sets behavior for the Yii framework utilizing the Modified Preorder Tree Traversal algorithm.