message: Add missing tf
diff: @@ -442,7 +442,7 @@ def set_memory_growth(device, enable):
  For example:
  ```python
  - physical_devices = config.experimental.list_physical_devices('GPU')
  + physical_devices = tf.config.experimental.list_physical_devices('GPU')
  assert len(physical_devices) > 0, "Not enough GPU hardware devices available"
  tf.config.experimental.set_memory_growth(physical_devices[0], True)
  ```
  