Missing the instruction about how to use an insecure Docker registry

Below is the guide for integrating Harbor with KuebSphere. But as I mentioned in the title, there's a crucial part that is missing.

https://kubesphere.com.cn/en/docs/devops-user-guide/how-to-integrate/harbor/

# References
If you don't know how to do it. Please see also [the official document](https://docs.docker.com/registry/insecure/).

/area devops

Open the Harbor integration guide at the linked KubeSphere documentation page and compare it with Docker's official insecure registry document. Add the missing usage instructions for an insecure Docker registry, then verify that the guide clearly explains the configuration needed for the Harbor integration.

Written by the indexing model from the issue text.