Adding the rst file to render IO under Fluid in paddlepaddle.org

doc/api/v2/fluid.rst

@@ -15,4 +15,4 @@ Fluid
     fluid/param_attr.rst
     fluid/profiler.rst
     fluid/regularizer.rst
-
+    fluid/io.rst

doc/api/v2/fluid/io.rst

+===========
+IO
+===========
+
+
+
+isParameter
+-----------
+..  autofunction:: paddle.v2.fluid.io.is_parameter
+    :noindex:

python/paddle/v2/fluid/io.py

@@ -11,6 +11,16 @@ __all__ = [
 
 
 def is_parameter(var):
+    """Check whether the variable is a Parameter
+
+    This function checks whether the input variable is a Parameter.
+
+    Args:
+        var : The input variable.
+
+    Returns:
+        boolean result whether the variable is a Parameter
+    """
     return isinstance(var, Parameter)