The interaction between a C# [Tool] script and Resources is not clearly documented

**Your Godot version:**

4.3

**Issue description:**

In GDScript, a @tool script can reference a non @tool resource object. In C#, as soon as a script is marked [Tool], any Resource derived custom classes it references must be marked [Tool] as well. This is non-trivial, and not clearly documented, as can be seen by the issues opened about it:

https://github.com/godotengine/godot/issues/80021
https://github.com/godotengine/godot/issues/80298
https://github.com/godotengine/godot/issues/85825

There is a pretty nice page discussing the use of [tool scripts in GDScript and C#](https://docs.godotengine.org/en/stable/tutorials/plugins/running_code_in_the_editor.html#important-information). However, due to the phrasing it is not obvious this applies to Resource objects as well.

**Suggestion**

Add a sentence to note that any custom Resource referenced by a C# Tool script must be marked [Tool] as well.

**URL to the documentation page (if already existing):**

https://docs.godotengine.org/en/stable/tutorials/plugins/running_code_in_the_editor.html#important-information