Added Imagick to readme

README.md

@@ -39,6 +39,10 @@ In order to use the Dropbox import from your server, you need a valid drop-ins a
 
 Lychee supports [Twitter Cards](https://dev.twitter.com/docs/cards) and [Open Graph](http://opengraphprotocol.org) for shared images (not albums). In order to use Twitter Cards you need to request an approval for your domain. Simply share an image with Lychee, copy its link and paste it in [Twitters Card Validator](https://dev.twitter.com/docs/cards/validation/validator).
 
+### Imagick
+
+Lychee uses [Imagick](http://www.imagemagick.org) when installed on your server. In this case you will benefit from a faster processing of your uploads, better looking thumbnails and intermediate sized images for small screen devices. You can disable the usage of [Imagick](http://www.imagemagick.org) in [the settings](docs/Settings.md).
+
 ### Plugins and Extensions
 
 The plugin-system of Lychee allows you to execute scripts, when a certain action fires. Plugins are hooks, which are injected directly into Lychee. [Plugin documentation »](docs/Plugins.md)