Respond to Helin's comments

Author: wangkuiyi

doc/build/docker_install.rst

@@ -20,36 +20,42 @@ For each version of PaddlePaddle, we release 4 variants of Docker images:
 |    gpu-noavx    |   no        |  yes  |
 +-----------------+-------------+-------+
 
-The following command line detects if your CPU supports :code:`AVX`.
+We run the following command on Linux to check if the CPU supports :code:`AVX`.
 
-..  code-block:: bash
+.. code-block:: bash
+
+   if cat /proc/cpuinfo | grep -i avx; then echo Yes; else echo No; fi
+
+On Mac OS X, we need to run
+
+.. code-block:: bash
 
-    if cat /proc/cpuinfo | grep -q avx ; then echo "Support AVX"; else echo "Not support AVX"; fi
+   sysctl -a | grep machdep.cpu.leaf7_features
 
 
 Once we determine the proper variant, we can cope with the Docker image tag name by appending the version number.  For example, the following command runs the AVX-enabled image of the most recent version:
 
-..  code-block:: bash
+.. code-block:: bash
 
     docker run -it --rm paddledev/paddle:cpu-latest /bin/bash
 
 To run a GPU-enabled image, you need to install CUDA and let Docker knows about it:
 
-..  code-block:: bash
+.. code-block:: bash
 
     export CUDA_SO="$(\ls /usr/lib64/libcuda* | xargs -I{} echo '-v {}:{}') $(\ls /usr/lib64/libnvidia* | xargs -I{} echo '-v {}:{}')"
     export DEVICES=$(\ls /dev/nvidia* | xargs -I{} echo '--device {}:{}')
     docker run ${CUDA_SO} ${DEVICES} -it paddledev/paddle:gpu-latest
 
 The default entry point of all our Docker images starts the OpenSSH server.  To run PaddlePaddle and to expose OpenSSH port to 2202 on the host computer:
 
-..  code-block:: bash
+.. code-block:: bash
 
     docker run -d -p 2202:22 paddledev/paddle:cpu-latest
 
 Then we can login to the container using username :code:`root` and password :code:`root`:
 
-..  code-block:: bash
+.. code-block:: bash
 
     ssh -p 2202 root@localhost
 

paddle/scripts/docker/Dockerfile.m4

@@ -4,7 +4,8 @@ MAINTAINER PaddlePaddle Dev Team <paddle-dev@baidu.com>
 # It is good to run apt-get install with Dockerfile RUN directive,
 # because if the following invocation to /root/build.sh fails, `docker
 # build` wouldn't have to re-install packages after we fix
-# /root/build.sh.
+# /root/build.sh.  For more about Docker build cache, please refer to
+# https://docs.docker.com/engine/userguide/eng-image/dockerfile_best-practices/#/build-cache.
 RUN apt-get update && \
     apt-get install -y cmake libprotobuf-dev protobuf-compiler git \
     libgoogle-glog-dev libgflags-dev libatlas-dev libatlas3-base g++ m4 python-pip \