adding silverstripe to cms list

README.md

@@ -189,6 +189,7 @@ CMS are a practical way to setup a website with many features. CMS often come wi
   * [october](http://octobercms.com/) - Free, open-source, self-hosted CMS platform based on the Laravel PHP Framework. ([Source code](https://github.com/octobercms/october)) `MIT`
   * [Pagekit](http://pagekit.com/) - A new modern CMS to create and share ([Source code](https://github.com/pagekit/pagekit)) - `MIT`
   * [Pico](http://picocms.org/) - A stupidly simple, blazing fast, flat file CMS. ([Source code](https://github.com/gilbitron/Pico)) `MIT`
+  * [SilverStripe](https://www.silverstripe.org) - easy to use CMS with powerful MVC framework underlying. `BSD`
   * [SPIP](http://www.spip.net/fr) - Publication system for the Internet. 
   * [Wordpress](https://wordpress.org/) - The worlds most-used blogging and CMS engine. ([Source code mirror](https://github.com/WordPress/WordPress)) `GPLv2`