add some comments

paddle/scripts/docker/README.md

@@ -94,7 +94,7 @@ docker build -t paddle:dev --build-arg UBUNTU_MIRROR=mirror://mirrors.ubuntu.com
 Given the development image `paddle:dev`, the following command builds PaddlePaddle from the source tree on the development computer (host):
 
 ```bash
-docker run --rm -v $PWD:/paddle -e "WITH_GPU=OFF" -e "WITH_AVX=ON" -e "WITH_TEST=OFF" -e "RUN_TEST=OFF" paddle:dev
+docker run --rm -v $PWD:/paddle -e "WITH_GPU=OFF" -e "WITH_AVX=ON" -e "WITH_TESTING=OFF" -e "RUN_TEST=OFF" paddle:dev
 ```
 
 This command mounts the source directory on the host into `/paddle` in the container, so the default entry point of `paddle:dev`, `build.sh`, could build the source code with possible local changes.  When it writes to `/paddle/build` in the container, it writes to `$PWD/build` on the host indeed.

paddle/scripts/docker/build.sh

@@ -44,6 +44,8 @@ fi
 make install
 pip install /usr/local/opt/paddle/share/wheels/*.whl
 
+# Since python v2 api import py_paddle module, the generation of paddle docs
+# depend on paddle's compilation and installation
 if [ ${WITH_DOC} == "ON" ]; then
     mkdir -p /paddle/build_doc
     pushd /paddle/build_doc