Add note on where the referenced affix example comes from

Author: Exanite

docs/for-contributors/Generator/name-processing.md

@@ -372,6 +372,7 @@ autocompleting `PerformanceCounterDescriptionARM`.
 
 Referenced affixes work the exact same as normal name affixes, but take advantage of C#'s nameof syntax.
 
+For example, from the SDL bindings:
 ```cs
 public struct GamepadBinding;