added the py311 to target-version config

[iamibi]

Description

The documentation currently doesn't share that python 3.11 is supported as part of the -t, --target-version flag. This PR updates the documentation to support that.

Checklist - did you ...

• Add an entry in CHANGES.md if necessary?
• Add / update tests if necessary?
• Add new / update outdated documentation?

Issue: #3897

[JelleZijlstra]

Thanks! Let's remove py37 from the list while we're at it.

Also, let's add a sentence like "You can run black --help and look for the --target-version option to see the full list of supported versions." so it's less likely we have to update this again.

[iamibi]

Thanks! Let's remove py37 from the list while we're at it.

Also, let's add a sentence like "You can run black --help and look for the --target-version option to see the full list of supported versions." so it's less likely we have to update this again.

sure.