Link new Ragdoll Physics demo in Ragdoll system

Author: Calinou

tutorials/physics/ragdoll_system.rst

@@ -17,6 +17,9 @@ In this tutorial, we will be using the Platformer 3D demo to set up a ragdoll.
     `GitHub <https://github.com/godotengine/godot-demo-projects/tree/master/3d/platformer>`_
     or using the `Asset Library <https://godotengine.org/asset-library/asset/2748>`_.
 
+    You can also check out an example of a complete ragdoll setup in the
+    `Ragdoll Physics demo <https://github.com/godotengine/godot-demo-projects/tree/master/3d/ragdoll_physics>`_.
+
 Setting up the ragdoll
 ----------------------