Add info on the image package.

Author: jpsacha

scalafx-extras/src/main/scala/root-doc.creole

@@ -3,5 +3,7 @@ Helper methods and classes to simplify ScalaFX use.
 Package [[org.scalafx.extras `org.scalafx.extras`]] contains basic helper methods for running tasks on threads and
 showing messages.
 
+Package [[org.scalafx.extras.image `org.scalafx.extras.image`]] contains image display component with scrolling and zooming.
+
 Package [[org.scalafx.extras.mvcfx `org.scalafx.extras.mvcfx`]] contains classes for creating with UI components
 based on FXML.