Document for opendal-oli is needed

Do you think that add a document for opendal-oli is a good idea?

For me, I try to edit the config, but there is not a document for it (yeah the README is helpful but I still need to check the source code). I think maybe a detailed document will be helpful.

Start with the existing README and the source code that defines opendal-oli's configuration. Identify the configuration options needed to use the CLI and document them with practical examples. Done means users can configure opendal-oli without searching the source code.

Written by the indexing model from the issue text.