Updated C# and .NET docs supplement (markdown)

C#-and-.NET-docs-supplement.md

@@ -34,4 +34,14 @@ If an object being the wrong type is *exceptional*—the method can't handle it
 
 `class` in `where` clauses does not mean "not abstract", it means "reference type". Similarly, `struct` means "value type". There's a lot of complexity re: nullability, so [check the docs](https://learn.microsoft.com/en-us/dotnet/csharp/programming-guide/generics/constraints-on-type-parameters) if you're writing a generic method.
 
-TODO euler diagram
+TODO euler diagram
+
+## WinForms `Control.ResumeLayout` footgun
+
+```csharp
+// works
+groupBox.ResumeLayout(performLayout: false);
+groupBox.PerformLayout();
+// breaks subtly
+groupBox.ResumeLayout(performLayout: true);
+```