!13885 fix quant _partial_init example

From: @yuchaojie
Reviewed-by: @zhoufeng54,@kisnwang
Signed-off-by: @zhoufeng54

mindspore/nn/layer/quant.py

@@ -112,6 +112,9 @@ def _partial_init(cls_or_self, **kwargs):
     constructor arguments, but different instances.
 
     Examples:
+        >>> class Foo:
+        >>>     def __init__(self, a, b, answer):
+        >>>         pass
         >>> Foo.partial_init = classmethod(_partial_init)
         >>> foo_builder = Foo.partial_init(a=3, b=4).partial_init(answer=42)
         >>> foo_instance1 = foo_builder()