Link new Ragdoll Physics demo in Ragdoll system

- Add tip to select all PhysicalBone3D nodes in the section
  about changing collision layers/masks.

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
 ----------------------
 
@@ -268,6 +271,13 @@ You can find the GridMap in the 3D platformer demo in ``stage/grid_map.scn``.
 The coin's Area3D node (on which the layers and masks must be adjusted)
 can be found at ``coin/coin.tscn``.
 
+.. tip::
+
+    To select all PhysicalBone3D nodes quickly, enter ``t:PhysicalBone3D`` in the
+    search bar at the top of the scene tree dock. This filters the scene tree
+    to only show PhysicalBone3D nodes, which allows you to select them all at once
+    using :kbd:`Shift + Left mouse button` on the first and last entries.
+
 If this is not done, collision will behave incorrectly as the player will collide
 with its own (inactive) ragdoll. This can cause the player to wildly
 bounce around or get stuck.