Tutorial or docs on human skin/hair shaders

**Your Godot version:**
4.0.2

**Issue description:**
It's supposedly possible to achieve proper skin/hair look with built-in materials and shaders. The problem is, next to no one knows how to do it. Please document.

Raised in a comment in https://github.com/godotengine/godot-proposals/issues/6900 which was closed because OP deleted comments/other assets were found, so I'm opening an issue solely for the **documentation part**

**URL to the documentation page (if already existing):**
N/A