update whats new

dist/preview release/what's new.md

@@ -126,6 +126,7 @@
 - Removed element IDs from viewer's templates to allow muitiple viewers in a single page [#4500](https://github.com/BabylonJS/Babylon.js/issues/4500) ([RaananW](https://github.com/RaananW))
 - Viewer is not using Engine.LastCreatedScene anymore, to support multiple viewers in a single page [#4500](https://github.com/BabylonJS/Babylon.js/issues/4500) ([RaananW](https://github.com/RaananW))
 - Template location was ignored if html was defined ([RaananW](https://github.com/RaananW))
+- Drag and Drop only worked if a model was already loaded before ([RaananW](https://github.com/RaananW))
 
 ### Loaders