add badge with last commit to README

Author: tabacitu

README.md

@@ -11,6 +11,7 @@
     <br>
     <a href="https://packagist.org/packages/backpack/crud" title="Latest Version on Packagist"><img src="https://img.shields.io/packagist/v/backpack/crud.svg?style=flat-square"></a>
     <a href="https://packagist.org/packages/backpack/crud" title="Total Downloads"><img src="https://img.shields.io/packagist/dt/backpack/crud.svg?style=flat-square"></a>
+    <a href="https://github.com/Laravel-Backpack/CRUD/commits/master" title="Last commit"><img alt="GitHub last commit" src="https://img.shields.io/github/last-commit/laravel-backpack/crud"></a>
     <a href="https://scrutinizer-ci.com/g/laravel-backpack/crud" title="Quality Score"><img src="https://img.shields.io/scrutinizer/g/laravel-backpack/crud.svg?style=flat-square"></a>
     <a href="https://travis-ci.org/Laravel-Backpack/CRUD" title="Build Status"><img src="https://img.shields.io/travis/Laravel-Backpack/CRUD/master.svg?style=flat-square"></a>
     <a href="https://styleci.io/repos/53581270" title="Style CI"><img src="https://styleci.io/repos/53581270/shield"></a>