docker pull很慢解決辦法，切換docker源

##使用阿里雲鏡像加速器
[root@localhost ~]# mkdir -p /etc/docker
[root@localhost ~]# tee /etc/docker/daemon.json <<-'EOF'
{
  "registry-mirrors": ["https://9cpn8tt6.mirror.aliyuncs.com"]
}
EOF
[root@localhost ~]# systemctl daemon-reload
[root@localhost ~]# systemctl restart docker