New tree (#1525)

* update 1_6 release

* fix readme
test=document_preview

* add new tree index

README.md

@@ -2,6 +2,7 @@
 
 English | [简体中文](./README_cn.md)
 
+
 # Introduction
 FluidDoc consolidates all the documentations related to Paddle. It supplies the contents to PaddlePaddle.org via CI. 
 

doc/fluid/api_cn/index_cn.rst

-=====
-API
-=====
+=============
+API Reference
+=============
 
 ..  toctree::
     :maxdepth: 1
 
-    ../api_guides/index_cn.rst
+    ../api_guides/index.rst
+    fluid_cn.rst
     api_tree_cn.rst
-
+    average_cn.rst
+    backward_cn.rst
+    clip_cn.rst
+    data_feeder_cn.rst
+    dataset_cn.rst
+    dygraph_cn.rst
+    executor_cn.rst
+    index_cn.rst
+    initializer_cn.rst
+    io_cn.rst
+    layers_cn.rst
+    metrics_cn.rst
+    nets_cn.rst
+    optimizer_cn.rst
+    profiler_cn.rst
+    regularizer_cn.rst
+    transpiler_cn.rst
+    unique_name_cn.rst