Document which versions of quality-checker work with which Drupal versions

[malcomio]

I was able to install 1.3.0 on a Drupal 9 codebase, but on an 8.9.1 codebase, I got these errors:

  Problem 1
    - Installation request for vijaycs85/drupal-quality-checker ^1.3 -> satisfiable by vijaycs85/drupal-quality-checker[1.3.0].
    - Conclusion: remove symfony/console v3.4.42
    - Conclusion: don't install symfony/console v3.4.42
    - vijaycs85/drupal-quality-checker 1.3.0 requires sebastian/phpcpd ^5.0 -> satisfiable by sebastian/phpcpd[5.0.0, 5.0.1, 5.0.2, 5.0.x-dev].
    - sebastian/phpcpd 5.0.0 requires symfony/console ^4.0|^5.0 -> satisfiable by symfony/console[4.0.x-dev, 4.1.x-dev, 4.2.x-dev, 4.3.x-dev, 4.4.x-dev, 5.0.x-dev, 5.1.x-dev, v4.0.0, v4.0.0-BETA1, v

I was able to install 1.2.1 with Drupal 8.9.1