add deprecated msg to py_readers, test=release/1.6 (#20212)

Author: sneaxiy

python/paddle/fluid/layers/io.py

@@ -667,7 +667,7 @@ def network(reader):
     """
     logging.warn(
         'paddle.fluid.layers.py_reader() may be deprecated in the near future. '
-        'Please use paddle.fluid.io.PyReader() instead.')
+        'Please use paddle.fluid.io.DataLoader.from_generator() instead.')
     return _py_reader(
         capacity=capacity,
         shapes=shapes,
@@ -747,6 +747,9 @@ def network(img, label):
              except fluid.core.EOFException:
                  reader.reset()
     """
+    logging.warn(
+        'paddle.fluid.layers.create_py_reader_by_data() may be deprecated in the near future. '
+        'Please use paddle.fluid.io.DataLoader.from_generator() instead.')
     return _py_reader(
         capacity=capacity,
         shapes=None,