Indicate when setters are called

**Your Godot version:** v4.1.2.stable.official [399c9dc39]

**Issue description:**

I think that we should add that this is the order of calls: `_init > getters > setters > _enter_tree > _ready`.

So inner children whose properties are exported through its parent and have a setter, must be instantiated on `_init`.

**URL to the documentation page (if already existing):** https://docs.godotengine.org/en/stable/tutorials/scripting/gdscript/gdscript_basics.html#properties-setters-and-getters