!7009 Add import for ops

Merge pull request !7009 from liuyang/ops

mindspore/ops/__init__.py

@@ -18,6 +18,9 @@ Operators can be used in the construct function of Cell.
 
 Examples:
 
+    >>> from mindspore.ops import operations as P
+    >>> from mindspore.ops import composite as C
+    >>> from mindspore.ops import functional as F
     >>> import mindspore.ops as ops
 
 Note: