Fix example code bugs (#42739)

* update readme test=document_fix

* fix api docs bugs test=document_fix

python/paddle/nn/utils/weight_norm_hook.py

@@ -219,8 +219,14 @@ def remove_weight_norm(layer, name='weight'):
 
             conv = Conv2D(3, 5, 3)
             wn = weight_norm(conv)
-          remove_weight_norm(conv)
             print(conv.weight_g)
+            # Parameter containing:
+            # Tensor(shape=[5], dtype=float32, place=Place(gpu:0), stop_gradient=False,
+            #        [0., 0., 0., 0., 0.])
+            # Conv2D(3, 5, kernel_size=[3, 3], data_format=NCHW)
+
+            remove_weight_norm(conv)
+            # print(conv.weight_g)
             # AttributeError: 'Conv2D' object has no attribute 'weight_g'
     """
     for k, hook in layer._forward_pre_hooks.items():