docs: fix broken link to config documentation in README

[john-s-lin]

Description

A description of the change, what it does, and why it was made. If relevant (such as any change that modifies the UI), please provide screenshots of the changes:

Fixes a broken link to configuration documentation in the README.

Previous link:

New link (one level up):

Checklist

If relevant, ensure the following have been met:

• Areas your change affects have been linted using rustfmt (cargo fmt)
• The change has been tested and doesn't appear to cause any unintended breakage
• Documentation has been added/updated if needed (README.md, help menu, doc pages, etc.)
• The pull request passes the provided CI pipeline
• There are no merge conflicts
• If relevant, new tests were added (don't worry too much about coverage)

[ClementTsang]

Thanks for catching this!

@all-contributors please add @john-s-lin for docs.

[allcontributors]

@ClementTsang

I couldn't determine any contributions to add, did you specify any contributions?
Please make sure to use valid contribution names.

I've put up a pull request to add @john-s-lin! 🎉