Added patch note for SDL_GDKGetDefaultUser()

WhatsNew.txt

@@ -1,9 +1,18 @@
 
 This is a list of major changes in SDL's version history.
 
+---------------------------------------------------------------------------
+2.30.0:
+---------------------------------------------------------------------------
+
+Xbox:
+* Added the function SDL_GDKGetDefaultUser()
+
+
 ---------------------------------------------------------------------------
 2.28.2:
 ---------------------------------------------------------------------------
+
 General:
 * Added the hint SDL_HINT_JOYSTICK_WGI to control whether to use Windows.Gaming.Input for controllers