I'm not sure why, but for some reason, packagist is only recognizing the 6.x series of tags, and even of those, it's ignoring `6.0.0-beta1`. Not sure why. We could choose to just not mention it, but it's odd.

https://packagist.org/packages/drush/drush
https://github.com/drush-ops/drush/tags

Any thoughts on why this might be, @Seldaek? If it's unexpected behavior, I'm happy to open up an issue