add CDNJS version badge in README.md (#422)

This badge will show the version on CDNJS!

Author: pvnr0082t

README.md

@@ -5,6 +5,7 @@
 [![Dependency Status](http://www.versioneye.com/user/projects/53f742dce09da3467d000389/badge.svg?style=flat)](http://www.versioneye.com/user/projects/53f742dce09da3467d000389)
 [![Dependency Status](http://www.versioneye.com/user/projects/53f742e2e09da3dca800038f/badge.svg?style=flat)](http://www.versioneye.com/user/projects/53f742e2e09da3dca800038f)
 [![Codacy Badge](https://www.codacy.com/project/badge/1f8565ed2e554e4fa952ec4da6a2080b)](https://www.codacy.com/public/orthes/mediumeditorinsertplugin)
+[![CDNJS](https://img.shields.io/cdnjs/v/medium-editor-insert-plugin.svg)](https://cdnjs.com/libraries/medium-editor-insert-plugin)
 
 This plugin expands capabilities of [MediumEditor](https://github.com/yabwe/medium-editor) (a clone of medium.com WYSIWYG editor) and it enables users to insert into the editor various types of content (depending on available addons).