!1673 update r0.3 relase notes

Merge pull request !1673 from guozhijian/update_r0.3_release_notes

README.md

@@ -76,7 +76,7 @@ For installation using `pip`, take `CPU` and `Ubuntu-x86` build version as an ex
 1. Download whl from [MindSpore download page](https://www.mindspore.cn/versions/en), and install the package.
 
     ```
-    pip install https://ms-release.obs.cn-north-4.myhuaweicloud.com/0.3.0-alpha/MindSpore/cpu/x86_ubuntu/mindspore-0.3.0-cp37-cp37m-linux_x86_64.whl
+    pip install https://ms-release.obs.cn-north-4.myhuaweicloud.com/0.3.0-alpha/MindSpore/cpu/ubuntu_x86/mindspore-0.3.0-cp37-cp37m-linux_x86_64.whl
     ```
 
 2. Run the following command to verify the install.

docker/mindspore-cpu/0.3.0-alpha/Dockerfile

@@ -64,4 +64,4 @@ RUN mkdir -pv /root/.pip \
     && echo "index-url=http://mirrors.aliyun.com/pypi/simple/" >> /root/.pip/pip.conf
 
 # Install MindSpore cpu whl package
-RUN pip install --no-cache-dir https://ms-release.obs.cn-north-4.myhuaweicloud.com/0.3.0-alpha/MindSpore/cpu/x86_ubuntu/mindspore-0.3.0-cp37-cp37m-linux_x86_64.whl
+RUN pip install --no-cache-dir https://ms-release.obs.cn-north-4.myhuaweicloud.com/0.3.0-alpha/MindSpore/cpu/ubuntu_x86/mindspore-0.3.0-cp37-cp37m-linux_x86_64.whl

docker/mindspore-gpu/0.3.0-alpha/Dockerfile

@@ -80,4 +80,4 @@ RUN cd /tmp \
     && rm -f /tmp/openmpi-3.1.5.tar.gz
 
 # Install MindSpore cuda-10.1 whl package
-RUN pip install --no-cache-dir https://ms-release.obs.cn-north-4.myhuaweicloud.com/0.3.0-alpha/MindSpore/gpu/cuda-10.1/mindspore_gpu-0.3.0-cp37-cp37m-linux_x86_64.whl
+RUN pip install --no-cache-dir https://ms-release.obs.cn-north-4.myhuaweicloud.com/0.3.0-alpha/MindSpore/gpu/ubuntu_x86/cuda-10.1/mindspore_gpu-0.3.0-cp37-cp37m-linux_x86_64.whl