Clarify that the SDL_GetStringRule means that SDL will automatically free the memory later.

include/SDL3/SDL_mouse.h

@@ -152,7 +152,7 @@ extern SDL_DECLSPEC SDL_MouseID *SDLCALL SDL_GetMice(int *count);
  *
  * This function returns "" if the mouse doesn't have a name.
  *
- * The returned string follows the SDL_GetStringRule.
+ * The returned string follows the SDL_GetStringRule, and will be automatically freed later.
  *
  * \param instance_id the mouse instance ID.
  * \returns the name of the selected mouse, or NULL on failure; call