message: Revise GPU delegate advanced documentation
diff: @@ -314,7 +314,7 @@ avoidable memory copies.
  Assuming the image input is in GPU memory, it must first be converted to a
  `MTLBuffer` object for Metal. You can associate a TfLiteTensor to a
  user-prepared `MTLBuffer` with `TFLGpuDelegateBindMetalBufferToTensor()`. Note
  -that `TFLGpuDelegateBindMetalBufferToTensor()` must be called before
  +that `TFLGpuDelegateBindMetalBufferToTensor()` must be called after
  `Interpreter::ModifyGraphWithDelegate()`. Additionally, the inference output is,
  by default, copied from GPU memory to CPU memory. This behavior can be turned
  off by calling `Interpreter::SetAllowBufferHandleOutput(true)` during
  @@ -328,11 +328,19 @@ initialization.
  // Prepare GPU delegate.
  auto* delegate = TFLGpuDelegateCreate(nullptr);
  -interpreter->SetAllowBufferHandleOutput(true); // disable default gpu->cpu copy
  -if (!TFLGpuDelegateBindMetalBufferToTensor(delegate, interpreter->inputs()[0], user_provided_input_buffer)) return false;
  -if (!TFLGpuDelegateBindMetalBufferToTensor(delegate, interpreter->outputs()[0], user_provided_output_buffer)) return false;
  +
  if (interpreter->ModifyGraphWithDelegate(delegate) != kTfLiteOk) return false;
  +interpreter->SetAllowBufferHandleOutput(true); // disable default gpu->cpu copy
  +if (!TFLGpuDelegateBindMetalBufferToTensor(
  + delegate, interpreter->inputs()[0], user_provided_input_buffer)) {
  + return false;
  +}
  +if (!TFLGpuDelegateBindMetalBufferToTensor(
  + delegate, interpreter->outputs()[0], user_provided_output_buffer)) {
  + return false;
  +}
  +
  // Run inference.
  if (interpreter->Invoke() != kTfLiteOk) return false;
  ```
  @@ -341,6 +349,10 @@ Note: Once the default behavior is turned off, copying the inference output from
  GPU memory to CPU memory requires an explicit call to
  `Interpreter::EnsureTensorDataIsReadable()` for each output tensor.
  +Note: This also works for quantized models, but you still need to a **float32
  +sized buffer with float32 data**, because the buffer will be bound to the
  +internal dequantized buffer.
  +
  ## Tips and Tricks
  * Some operations that are trivial on the CPU may be high cost on a GPU. One
  