fix write new op index (#626)

doc/fluid/advanced_usage/development/new_op/index_en.rst

@@ -2,9 +2,9 @@
 Write New Operators
 ###################
 
-- `How to write new operator <../../../advanced_usage/development/new_op_en.html>`_ ：guides to write new operators
+- `How to write new operator <new_op_en.html>`_ ：guides to write new operators
 
-- `op notes <../../../advanced_usage/development/op_notes_en.html>`_ ：notes on developing new operators
+- `op notes <op_notes_en.html>`_ ：notes on developing new operators
 
 .. toctree::
    :hidden: