Document filename requirements in C# global classes

- Flesh out the introduction.

tutorials/scripting/c_sharp/c_sharp_global_classes.rst

@@ -3,8 +3,11 @@
 C# global classes
 =================
 
-Global classes (also known as named scripts) are types registered in Godot's editor so they can be used
-more conveniently.
+Global classes (also known as named scripts) are types registered in Godot's
+editor so they can be used more conveniently.
+:ref:`In GDScript <doc_gdscript_basics_class_name>`, this is achieved
+using the ``class_name`` keyword at the top of a script. This page describes how
+to achieve the same effect in C#.
 
 - Global classes show up in the *Add Node* and *Create Resource* dialogs.
 - If an :ref:`exported property <doc_c_sharp_exports>` is a global class, the
@@ -22,6 +25,12 @@ Global classes are registered with the ``[GlobalClass]`` attribute.
     {
     }
 
+.. warning::
+
+    The file name must match the class name in **case-sensitive** fashion.
+    For example, a global class named "MyNode" must have a file name of
+    ``MyNode.cs``, not ``myNode.cs``.
+
 The ``MyNode`` type will be registered as a global class with the same name as the type's name.
 
 .. image:: img/globalclasses_addnode.webp
@@ -84,8 +93,7 @@ will let you create and load instances of this type easily.
 .. warning::
 
     The Godot editor will hide these custom classes with names that begin with the prefix
-    "Editor" in the 'Create New Node' or 'Create New Scene' dialog windows. The classes 
-    are available for instantiation at runtime via their class names, but are 
-    automatically hidden by the editor windows along with the built-in editor nodes used 
+    "Editor" in the "Create New Node" or "Create New Scene" dialog windows. The classes
+    are available for instantiation at runtime via their class names, but are
+    automatically hidden by the editor windows along with the built-in editor nodes used
     by the Godot editor.
-