Restore Matrix on the contact page

It looks like my old Internet provider was the source of all the
problems I used to have with this service.

It's viable again.

docs/en/contact.md

@@ -7,11 +7,11 @@ title: Contact
 
 # Contact
 
-Probably prefer [Github issues]({{ site.repository-url }}/issues) for bug tracking, feature requests and help. Github can also send you notifications on releases if you watch the project.
+Our bug tracker is [Github issues]({{ site.repository-url }}/issues).
 
-Otherwise, we have the following mailing lists:
+For support and/or general discussion, try our [chat on Matrix](https://matrix.ungleich.ch/#/room/#jool:ungleich.ch) or the [[email protected] mailing list](https://mail-lists.nic.mx/listas/listinfo/jool-list).
 
-- [email protected] ([Registration](https://mail-lists.nic.mx/listas/listinfo/jool-list)): General public discussion and news. Questions, requests and comments welcomed.
-- [email protected] ([Registration](https://mail-lists.nic.mx/listas/listinfo/jool-news)): To advertise new releases. Only the dev team can place mails here.
-- [[email protected]](mailto:[email protected]): A mail alias you can use to reach us developers only.
+If you want to be notified when new releases are available, [watch the project on Github](https://github.com/NICMx/Jool) or subscribe to the [news mailing list](https://mail-lists.nic.mx/listas/listinfo/jool-news).
+
+There's also [[email protected]](mailto:[email protected]), which is a mail alias you can use to reach us developers only.