Clarify GodotSteam #13
Description
While there is a fork of Godot that includes GodotSteam built-in directly, most projects use it via the GDNative (godot 3.x) or GDExtension (godot 4.x) plug-ins. It might be a good idea to note that you can access GodotSteam via the plugins in MODS.md so people don't end up having to fumble around with Godot forks when it's not necessary.