Add IntelliJ docs on external tools and file watcher

[ruslaniv]

Revert deleted documentation on setting up Black using IntelliJ external tool or file watcher utilities

Issue: https://github.com/psf/black/issues/3271

Description

Add documentation section on how to set up black in IntelliJ products using either File Watcher or External Tools utilities

Checklist

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• [x] Add new / update outdated documentation?