Mercure Notifier integration doc review

This is more of an outreach issue, feel free to close once sighted.

I've worked on putting together Symfony Notifier → integration for Drupal, including support and validation for Mercure.

Specifically for Mercure, and this Drupal Mercure project, I've written up a doc page @ https://comms.docs.contrib.social/chatter/services/mercure

Let me know if you (maintainers) here desire any additions/modifications of any size to this page.

( Unfortunately you're not able to modify it directly. )

Thanks for the project!