[dotnet] add documents for http, zookeeper, consul and nacos registration. And updated README.

[Han G]

Hi folks,

I’ve created a PR to add documents for http, zookeeper, consul and nacos 
registration. And updated README. Please help to review/comment. Thanks for 
your time!

https://github.com/apache/shenyu-client-dotnet/pull/35

Thanks,
Han