安装报错信息如下：
ERROR: Could not find a version that satisfies the requirement PIL (from versions: none)
ERROR: No matching distribution found for PIL
解决方式：
pip install PIL-i https://pypi.tuna.tsinghua.edu.cn/simple/
pip install 包名-i http://pypi.douban.com/simple/ --trusted-host pypi.douban.com