Docs: GPU: Added documentation on the WinPixEventRuntime.dll requirement to affected functions.

include/SDL3/SDL_gpu.h

@@ -2945,6 +2945,11 @@ extern SDL_DECLSPEC void SDLCALL SDL_SetGPUTextureName(
  *
  * Useful for debugging.
  *
+ * On Direct3D 12, using SDL_InsertGPUDebugLabel will cause validation errors
+ * unless you have WinPixEventRuntime.dll in your PATH.
+ * See [here](https://devblogs.microsoft.com/pix/winpixeventruntime/) for
+ * instructions on how to obtain it.
+ *
  * \param command_buffer a command buffer.
  * \param text a UTF-8 string constant to insert as the label.
  *
@@ -2963,6 +2968,11 @@ extern SDL_DECLSPEC void SDLCALL SDL_InsertGPUDebugLabel(
  * Each call to SDL_PushGPUDebugGroup must have a corresponding call to
  * SDL_PopGPUDebugGroup.
  *
+ * On Direct3D 12, using SDL_PushGPUDebugGroup will cause validation errors
+ * unless you have WinPixEventRuntime.dll in your PATH.
+ * See [here](https://devblogs.microsoft.com/pix/winpixeventruntime/) for
+ * instructions on how to obtain it.
+ *
  * On some backends (e.g. Metal), pushing a debug group during a
  * render/blit/compute pass will create a group that is scoped to the native
  * pass rather than the command buffer. For best results, if you push a debug
@@ -2982,6 +2992,11 @@ extern SDL_DECLSPEC void SDLCALL SDL_PushGPUDebugGroup(
 /**
  * Ends the most-recently pushed debug group.
  *
+ * On Direct3D 12, using SDL_PopGPUDebugGroup will cause validation errors
+ * unless you have WinPixEventRuntime.dll in your PATH.
+ * See [here](https://devblogs.microsoft.com/pix/winpixeventruntime/) for
+ * instructions on how to obtain it.
+ *
  * \param command_buffer a command buffer.
  *
  * \since This function is available since SDL 3.2.0.