Add docker pulls badge counter

Author: elgalu

CHANGELOG.md

@@ -8,7 +8,7 @@ Note image ids also change after scm-source.json has being updated which trigger
     docker exec grid versions
 
 ## 3.3.1-p5
- + **Changes:** https://github.com/elgalu/docker-selenium/compare/e5f198e1486630c19283d...master (2017-04-24)
+ + **Changes:** https://github.com/elgalu/docker-selenium/compare/e5f198e1486630c19283d...c4e8df12781eb031795ea6 (2017-04-24)
     + Guard transfer-logs.sh when -e CHROME=false
     + Chore: Tests minor cleanups
     + Chore: Add /logo.png so some apps can grab it

README.md

@@ -3,6 +3,7 @@
 
 [![Build Status](https://travis-ci.org/elgalu/docker-selenium.svg?branch=master)](https://travis-ci.org/elgalu/docker-selenium "Travis CI")
 [![Gitter](https://badges.gitter.im/Join Chat.svg)](https://gitter.im/elgalu/docker-selenium?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge&utm_content=badge "Chat support")
+[![Docker Pulls](https://img.shields.io/docker/pulls/elgalu/selenium.svg)](https://hub.docker.com/r/elgalu/selenium/tags/)
 [![Docker](https://images.microbadger.com/badges/version/elgalu/selenium.svg)](https://microbadger.com/images/elgalu/selenium "Docker Badge")
 
 * selenium server grid with 2 nodes (chrome & firefox)