Particle Shader Descriptions

**Your Godot version:**
4.1

**Issue description:**

Particle Shaders descriptions are not substantial enough. For example, the TRANSFORM description is: "Particle transform." I have no idea really what this means but looking online there is some information about the rotation, position, sheer and size but the documentation does not talk about this at all.

However, what I really need documentation on is the emit_subparticle. Could the creators expand on, what the inputs are, xform, and custom does not give any information. "Forces to emit a particle from a sub-emitter." Does that mean just a single particle? How can we emit GPU particles where the GpuParticles.Amount > 1?

**URL to the documentation page (if already existing):**
https://docs.godotengine.org/en/stable/tutorials/shaders/shader_reference/particle_shader.html#process-functions