fix doc in stream_guard

DesmonDay · DesmonDay · commit c364df106b03 · 2021-09-10T05:02:08.000Z
diff --git a/python/paddle/device/cuda/__init__.py b/python/paddle/device/cuda/__init__.py
@@ -159,6 +159,8 @@ def stream_guard(stream=None):
 
     Examples:
         .. code-block:: python
+
+            # required: gpu
             import paddle
             
             s = paddle.device.cuda.Stream()
