[Improve][Sort] Add some document of Redis connector about using as source

[liaosunny123]

Description

There is some document of using Redis Connector as Sink, can add some document of using Redis Connector as source?

InLong Component

InLong Sort

Are you willing to submit PR?

• [ ] Yes, I am willing to submit a PR!

Code of Conduct

• [X] I agree to follow this project's Code of Conduct