It has to be done on packagist site. I wanted to send a PR because I thought it's part of composer.json. See Tomas Votruba's blogpost https://tomasvotruba.com/blog/2017/07/03/how-to-deprecate-php-package-without-leaving-anyone-behind/#3.-inform-people-on-all-possible-places-they-can-meet-your-package
It has to be done on packagist site. I wanted to send a PR because I thought it's part of composer.json.
See Tomas Votruba's blogpost https://tomasvotruba.com/blog/2017/07/03/how-to-deprecate-php-package-without-leaving-anyone-behind/#3.-inform-people-on-all-possible-places-they-can-meet-your-package