Synchronize Chinese and English DOC of API:layers.sum (#1507)

Fix fluid.layers.data of example code, Synchronize Chinese and English DOC of API:layers.sum.

doc/fluid/api_cn/layers_cn/sum_cn.rst

@@ -48,13 +48,28 @@ sum
 **代码示例：**
 
 .. code-block:: python
-
-    import paddle.fluid as fluid
-    import paddle.fluid.layers as layers
-    input0 = layers.data(name="input0", shape=[13, 11], dtype='float32')
-    input1 = layers.data(name="input1", shape=[13, 11], dtype='float32')
-    out = layers.sum([input0,input1])
-
+	
+	import paddle.fluid as fluid
+	input0 = fluid.layers.fill_constant(shape=[2, 3], dtype='int64', value=5)
+	input1 = fluid.layers.fill_constant(shape=[2, 3], dtype='int64', value=3)
+	sum = fluid.layers.sum([input0, input1])
+
+	#用户可以通过executor打印出求和的结果
+	out = fluid.layers.Print(sum, message="the sum of input0 and input1: ")
+	exe = fluid.Executor(fluid.CPUPlace())
+	exe.run(fluid.default_main_program())
+
+	#打印出的数据为：
+	1570701754	the sum of input0 and input1: 	The place is:CPUPlace
+	Tensor[sum_0.tmp_0]
+		shape: [2,3,]
+		dtype: l
+		data: 8,8,8,8,8,8,
+
+	#输出了shape为[2,3]的Tensor，与输入的shape一致
+	#dtype为对应C++数据类型，在不同环境下可能显示值不同，但本质相同
+	#例如：如果Tensor中数据类型是int64，则对应的C++数据类型为int64_t，所以dtype值为typeid(int64_t).name()，
+	#      其在MacOS下为'x'，linux下为'l'，Windows下为'__int64'，都表示64位整型变量