doc(services/redb): add doc for redb service backend

[oowl]

add missing doc for #2526

[oowl]

Maybe we need a GitHub issue or PR template so that we can make sure our PR description is clear and understandable. cc @Xuanwo

[Xuanwo]

GitHub issue or PR template so that we can make sure our PR description is clear and understandable.

template is just a template which can't make sure description is clear and understandable. OpenDAL is a small community that most problems can be resolved by asking.

[Xuanwo]

Thanks!

[oowl]

GitHub issue or PR template so that we can make sure our PR description is clear and understandable.

template is just a template which can't make sure description is clear and understandable. OpenDAL is a small community that most problems can be resolved by asking.

I mean that If we have a PR template, it will reduce the workload of contributors. By defining a format for describing PRs, we can guide contributors to include all necessary information in their PRs, such as describing the problem they fixed, indicating if a test file needs to be added, and specifying if documentation needs to be updated. This will make it easier for reviewers to understand the intent of the PR and increase the chances of it being accepted.

[Xuanwo]

This will make it easier for reviewers to understand the intent of the PR and increase the chances of it being accepted.

OpenDAL is not yet at a stage where reviewers require complex information. All the pull requests we have received so far are small and straightforward. We will only ask for clarification when necessary, rather than burdening contributors with unnecessary requests.

While I acknowledge that this is a good idea and considered best practice, I don't believe it's necessary for OpenDAL. Thank you. Maybe we will add this while OpenDAL has 500 contributors.