Sync SDL3 wiki -> header

include/SDL3/SDL_timer.h

@@ -183,6 +183,8 @@ typedef Uint32 SDL_TimerID;
  * \returns a timer ID or 0 if an error occurs; call SDL_GetError() for more
  *          information.
  *
+ * \threadsafety It is safe to call this function from any thread.
+ *
  * \since This function is available since SDL 3.0.0.
  *
  * \sa SDL_RemoveTimer