add disable_dygraph enable_dygraph en cn docs (#1869)

* add disable_dygraph enable_dygraph en cn docs
test=develop

* clean DS_Store
test=develop

.gitignore

+*.DS_Store
 .vscode/
 /doc/fluid/menu.zh.json
 /doc/fluid/menu.en.json

doc/fluid/api/fluid.rst

@@ -20,10 +20,12 @@ fluid
     fluid/DataFeeder.rst
     fluid/default_main_program.rst
     fluid/default_startup_program.rst
+    fluid/disable_dygraph.rst
     fluid/device_guard.rst
     fluid/DistributeTranspiler.rst
     fluid/DistributeTranspilerConfig.rst
     fluid/embedding.rst
+    fluid/enable_dygraph.rst
     fluid/ExecutionStrategy.rst
     fluid/Executor.rst
     fluid/global_scope.rst

doc/fluid/api/fluid/disable_dygraph.rst

+..  THIS FILE IS GENERATED BY `gen_doc.{py|sh}`
+    !DO NOT EDIT THIS FILE MANUALLY!
+
+.. _api_fluid_disable_dygraph:
+
+disable_dygraph
+---------------
+
+..  autofunction:: paddle.fluid.disable_dygraph
+    :noindex:
+

doc/fluid/api/fluid/enable_dygraph.rst

+..  THIS FILE IS GENERATED BY `gen_doc.{py|sh}`
+    !DO NOT EDIT THIS FILE MANUALLY!
+
+.. _api_fluid_enable_dygraph:
+
+enable_dygraph
+--------------
+
+..  autofunction:: paddle.fluid.enable_dygraph
+    :noindex:
+

doc/fluid/api_cn/fluid_cn.rst

@@ -23,10 +23,12 @@ fluid
     fluid_cn/DataFeeder_cn.rst
     fluid_cn/default_main_program_cn.rst
     fluid_cn/default_startup_program_cn.rst
+    fluid_cn/disable_dygraph_cn.rst
     fluid_cn/device_guard_cn.rst
     fluid_cn/DistributeTranspiler_cn.rst
     fluid_cn/DistributeTranspilerConfig_cn.rst
     fluid_cn/embedding_cn.rst
+    fluid_cn/enable_dygraph_cn.rst
     fluid_cn/ExecutionStrategy_cn.rst
     fluid_cn/Executor_cn.rst
     fluid_cn/global_scope_cn.rst

doc/fluid/api_cn/fluid_cn/disable_dygraph_cn.rst

+.. _cn_api_fluid_disable_dygraph:
+
+disable_dygraph
+-------------------------------
+
+.. py:function:: paddle.fluid.disable_dygraph()
+
+该接口关闭动态图模式。
+
+返回：无
+
+**示例代码**
+
+.. code-block:: python
+
+    import paddle.fluid as fluid
+    import numpy as np
+    fluid.enable_dygraph()  # Now we are in dygraph mode
+    print(fluid.in_dygraph_mode())  # True
+    fluid.disable_dygraph()
+    print(fluid.in_dygraph_mode())  # False
+

doc/fluid/api_cn/fluid_cn/enable_dygraph_cn.rst

+.. _cn_api_fluid_enable_dygraph:
+
+enable_dygraph
+-------------------------------
+
+.. py:function:: paddle.fluid.enable_dygraph(place=None)
+
+该接口打开动态图模式。
+
+参数：
+  - **place** (fluid.CPUPlace 或 fluid.CUDAPlace，可选) - 执行动态图的设备数目。若为None，则设备根据paddle的编译方式决定。默认值为 ``None``。
+
+返回：无
+
+**示例代码**
+
+.. code-block:: python
+
+    import paddle.fluid as fluid
+    import numpy as np
+    fluid.enable_dygraph()  # Now we are in dygraph mode
+    print(fluid.in_dygraph_mode())  # True
+    fluid.disable_dygraph()
+    print(fluid.in_dygraph_mode())  # False
+