Clarify that SDL_HINT_JOYSTICK_ALLOW_BACKGROUND_EVENTS can be set anytime

Fixes https://github.com/libsdl-org/sdlwiki/issues/914

include/SDL3/SDL_joystick.h

@@ -46,8 +46,7 @@
  * and load appropriate drivers.
  *
  * If you would like to receive joystick updates while the application is in
- * the background, you should set the following hint before calling
- * SDL_Init(): SDL_HINT_JOYSTICK_ALLOW_BACKGROUND_EVENTS
+ * the background, you should set the SDL_HINT_JOYSTICK_ALLOW_BACKGROUND_EVENTS hint.
  *
  * SDL can provide virtual joysticks as well: the app defines an imaginary
  * controller with SDL_AttachVirtualJoystick(), and then can provide inputs