Fix document error.

python/paddle/v2/trainer.py

@@ -27,16 +27,21 @@ class SGD(object):
     SGD Trainer combines data reader, network topolopy and update_equation together
     to train/test a neural network.
 
-    :param update_equation: The optimizer object.
-    :type update_equation: paddle.v2.optimizer.Optimizer
     :param cost: Target cost that neural network should be optimized.
     :type cost: paddle.v2.config_base.Layer
     :param parameters: The parameters dictionary.
     :type parameters: paddle.v2.parameters.Parameters
+    :param update_equation: The optimizer object.
+    :type update_equation: paddle.v2.optimizer.Optimizer
     :param extra_layers: Some layers in the neural network graph are not
                          in the path of cost layer.
-    :param pserver_spec: pserver location, eg: localhost:3000
     :type extra_layers: paddle.v2.config_base.Layer
+    :param is_local: Whether trainning locally
+    :type is_local: bool
+    :param pserver_spec: pserver location, eg: localhost:3000
+    :type pserver_spec: string
+    :param use_etcd: Whether using etcd pserver.
+    :param use_etcd: bool
     """
 
     def __init__(self,