Sync SDL3 wiki -> header

[ci skip]

(cherry picked from commit 5212b82c4f03ecb6364b95baabb22a94ac24a878)

docs/README-gdk.md

@@ -32,7 +32,8 @@ The Windows GDK port supports the full set of Win32 APIs, renderers, controllers
 
 * Single-player games have some additional features available:
   * Call `SDL_GetGDKDefaultUser` to get the default XUserHandle pointer.
-  * `SDL_GetPrefPath` still works, but only for single-player titles.
+  * `SDL_GetPrefPath` and `SDL_Storage` still work, but only for single-player titles.
+    * To enable support for these APIs, use `SDL_SetHint` to set `SDL_GDK_SERVICE_CONFIGURATION_ID` to your SCID string at startup (it should be formatted like `"00000000-0000-0000-0000-000000000000"`)
 
   These functions mostly wrap around async APIs, and thus should be treated as synchronous alternatives. Also note that the single-player functions return on any OS errors, so be sure to validate the return values!