Sub-emitter information is too bare

**Your Godot version:**
4.3 b1

**Issue description:**
I'm trying to find pertinent information on the sub emitter page regarding how to set the proper amount, but there's not really a lot of information currently. It's easier to explain with an example so this is my case. I have a particle system for rain which I want a sub emitter to splatter a few particles to simulate the rain landing on the ground. These are the relevant settings:

RainGPUParticle2D:
- Amount: 50
- Sub Emitter Mode: At end
- Sub Emitter / Amount at end: 3

SubGPUParticle2D:
- Amount 150

I think anyone without prior knowledge or experience would try three values in this example(which is what I tried):

1. Sub Emitter Amount = 3: Only emits the splatter on very few rain particles(I'm guessing is 3 rain drops at a time). The "Amount at end" set on the RainGPUParticle2D.
2. Sub Emitter Amount = 50: Emits more than 3 splatter and not on every rain particle. The amount value set on RainGPUParticle2D.
3. Sub Emitter Amount = 150: Emits anywhere from 3 to 6 or more particles on each rain drop particle. The amount value set on RainGPUParticle2D multiplied by the "Amount at end" value set on RainGPUParticle2D / Sub emitter. This is what I would expect to be correct.

I think any other value than these three is a number that might be obvious to someone who knows the inner workings but if you don't. It would seem like a completely arbitrary number so you'd just have to guess through trial and error. Currently, the page in the documentation only discusses in the "Limitation" section that the amount of particles is capped by the amount set on the sub emitter. But it doesn't have any information on what the amount does and how both affect the other or how to find the right value for your case.

**URL to the documentation page (if already existing):**
https://docs.godotengine.org/en/stable/tutorials/3d/particles/subemitters.html