$ docker pull php:7.1-fpm-alpine
Error response from daemon: Get https://registry-1.docker.io/v2/: net/http: request canceled while waiting for connection (Client.Timeout exceeded while awaiting headers)
見到這段煩人的超時提示，就知道是網絡問題了，解決辦法是添加國內鏡像
https://docker.mirrors.ustc.edu.cn
https://hub-mirror.c.163.com
http://f1361db2.m.daocloud.io
鏡像可以添加多個
設置步驟:
Docker for Windows/Mac
Setting/Preference -> Daemon -> Registry mirrors