Document how to specify Black version when using a pre-commit hook

[akaihola]

@victorcui96, I think each pre-commit hook installs into its own environment so modifying your project's requirements.txt will have no effect. The above referencing issue has a fix though, so applying that in your pre commit config would look like:

 - repo: https://github.com/akaihola/darker
   rev: 1.5.1
   hooks:
     - id: darker
       args:
          - --line-length=120
       language_version: python3
       additional_dependencies: [black==22.10.0]

Originally posted by @leej3 in #412 (comment)