**Summary**
Add container registry mirorr.
**Use case**
1. not able to connect to docker official registry, but need to pull images
2. local mirror for either download accelerating or as private repo.
**Additional information**
My local config
```
# cat /etc/containers/registries.conf.d/mirror.conf
[[registry]]
location = "192.168.50.40:8088"
insecure = true
prefix = "docker.io"
```
I'll submit PR when I find best way managing mirrors.