Update to What's new 3.3 - catmull curve closing

dist/preview release/what's new.md

@@ -3,6 +3,9 @@
 ## Major updates
 
 ## Updates
+
+- Added the choice of [forming a closed loop](http://doc.babylonjs.com/how_to/how_to_use_curve3#catmull-rom-spline) to the catamull-rom-spline curve3 ([johnk](https://github.com/babylonjsguide))
+
 ## Bug fixes
 
 ## Breaking changes