Add log10 Chinese doc (PaddlePaddle#2842)

As the title

doc/paddle/api/alias_api_mapping

@@ -347,6 +347,7 @@ paddle.fluid.layers.add_position_encoding	paddle.nn.functional.add_position_enco
 paddle.nn.functional.common.cosine_similarity	paddle.nn.functional.cosine_similarity
 paddle.fluid.layers.floor	paddle.floor,paddle.tensor.floor,paddle.tensor.math.floor
 paddle.fluid.layers.log2    paddle.log2,paddle.tensor.log2,paddle.tensor.math.log2
+paddle.fluid.layers.log10    paddle.log10,paddle.tensor.log10,paddle.tensor.math.log10
 paddle.tensor.math.log1p    paddle.log1p,paddle.tensor.log1p
 paddle.fluid.layers.unstack	paddle.unstack,paddle.tensor.unstack,paddle.tensor.manipulation.unstack
 paddle.fluid.layers.rsqrt	paddle.rsqrt,paddle.tensor.rsqrt,paddle.tensor.math.rsqrt

doc/paddle/api/paddle/fluid/layers/log10_cn.rst

@@ -0,0 +1,47 @@
+.. _cn_api_fluid_layers_log10:
+
+log10
+-------------------------------
+
+.. py:function:: paddle.log10(x, name=None)
+
+
+
+
+
+Log10激活函数（计算底为10的对数）
+
+.. math::
+                  \\Out=log_{10} x\\
+
+
+参数:
+  - **x** (Tensor) – 该OP的输入为Tensor。数据类型为float32，float64。 
+  - **name** (str，可选) – 该参数供开发人员打印调试信息时使用，具体用法请参见 :ref:`api_guide_Name` ，默认值为None。
+
+返回：Log10算子底为10对数输出
+
+返回类型: Tensor - 该OP的输出为Tensor，数据类型为输入一致。
+
+
+**代码示例**
+
+..  code-block:: python
+
+  import paddle
+
+  # example 1: x is a float
+  x_i = paddle.to_tensor([[1.0], [10.0]])
+  res = paddle.log10(x_i) # [[0.], [1.0]]
+
+  # example 2: x is float32
+  x_i = paddle.full(shape=[1], fill_value=10, dtype='float32')
+  paddle.to_tensor(x_i)
+  res = paddle.log10(x_i)
+  print(res.numpy()) # [1.0]
+  
+  # example 3: x is float64
+  x_i = paddle.full(shape=[1], fill_value=10, dtype='float64')
+  paddle.to_tensor(x_i)
+  res = paddle.log10(x_i)
+  print(res.numpy()) # [1.0]