Added live example for 'Adding Regions' doc

Proposed changes
The live example shows a practical scenario where regions are added to the view depending on the model

Link to the issue: marionettejs#3209

docs/marionette.region.md

@@ -75,6 +75,8 @@ const MyApp = Application.extend({
 });
 ```
 
+[Live example](http://jsfiddle.net/marionettejs/9fburmb8/)
+
 For more information, see the
 [Application docs](./marionette.application.md#application-region).
 
@@ -259,6 +261,8 @@ myView.addRegions({
 });
 ```
 
+[Live example](http://jsfiddle.net/marionettejs/kjvzdyd6/)
+
 ## Removing Regions
 
 You can remove all of the regions from a view by calling `removeRegions` or you can remove a