Mention Autoloads on the style page

**Your Godot version:**
4.2.2

**Issue description:**
They aren't mentioned so users don't know the style for naming them (I guess they could follow the Autoload page?) Cuz I was looking at the code for an official demo project and the autoload there was in lower case

https://github.com/godotengine/godot-demo-projects/blob/4.2/networking/multiplayer_bomber/project.godot

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