Ragdoll tutorial leaves out a lot of info

**Your Godot version:**
3.2.3

**Issue description:**
I've been trying to figure out how to use ragdoll's, but the current tutorial really doesn't show you how. It shows you how to add ragdoll to a pre-made demo project, but not how you'd do it from scratch. I still haven't figured it out. I just flat-out don't understand how the skeleton node works from reading the tutorial and reference. The generate physical bones button doesn't do anything. If I need to create a skeleton/armature in a 3d modelling program, then the docs should point that out. Right now, it makes it seem like you can just generate a generic humanoid skeleton, and fit that to any mesh.

**URL to the documentation page (if already existing):**
https://docs.godotengine.org/en/stable/tutorials/physics/ragdoll_system.html