Sync SDL3 wiki -> header

include/SDL3/SDL_render.h

@@ -2130,6 +2130,9 @@ extern SDL_DECLSPEC void *SDLCALL SDL_GetRenderMetalCommandEncoder(SDL_Renderer
  * \returns 0 on success or a negative error code on failure; call
  *          SDL_GetError() for more information.
  *
+ * \threadsafety It is **NOT** safe to call this function from two threads at
+ *               once.
+ *
  * \since This function is available since SDL 3.0.0.
  */
 extern SDL_DECLSPEC int SDLCALL SDL_AddVulkanRenderSemaphores(SDL_Renderer *renderer, Uint32 wait_stage_mask, Sint64 wait_semaphore, Sint64 signal_semaphore);