Add SilverStripe as a framework integration to readme

SilverStripe ^4.0 and future 5.x ship with monolog out of the box

README.md

@@ -86,6 +86,7 @@ Bugs and feature request are tracked on [GitHub](https://github.com/Seldaek/mono
 - [Equip Framework](https://github.com/equip/framework) comes out of the box with Monolog.
 - [Yii 2](http://www.yiiframework.com/) is usable with Monolog via the [yii2-monolog](https://github.com/merorafael/yii2-monolog) or [yii2-psr-log-target](https://github.com/samdark/yii2-psr-log-target) plugins.
 - [Hawkbit Micro Framework](https://github.com/HawkBitPhp/hawkbit) comes out of the box with Monolog.
+- [SilverStripe 4](https://www.silverstripe.org/) come out of the box with Monolog.
 
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