Add document using zookeeper as the config center

## Why you need it?
Add document using zookeeper as the config center.
If you want to fix it, please comment "Please assign it to me" is this issue.

增加zookeeper作为配置中心的文档
如果你有兴趣修复这个问题的话, 请在下方留言 Please assign it to me

## How it could be?
A clear and concise description of what you want to happen. You can explain more about input of the feature, and output of it.

## Other related information
Add any other context or screenshots about the feature request here.

Start by reading the repository's existing documentation structure and any current configuration-center documentation. The issue provides no file or entry point, so first identify where this topic belongs; done means adding a clear document covering ZooKeeper as a configuration center and matching the site's documentation conventions.

Written by the indexing model from the issue text.