getting-started: Matrix chat for members

getting-started.md

@@ -55,6 +55,11 @@ You don't just use the co-op; you help run it. Decisions about models, pricing,
 privacy, and direction happen on our **Loomio forum**:
 
 - **[forum.inference.coop](https://forum.inference.coop)** — where members discuss and decide.
+- **[matrix.inference.coop](https://matrix.inference.coop)** — our Matrix chat server. Log in
+  with your co-op account (Cloudron SSO); your Matrix ID is `@username:inference.coop` and
+  works with any Matrix app (Element, Fluffychat, etc.). Every member is invited to the
+  **Inference Cooperative** space automatically — check your invites on first login. Your
+  existing Matrix account on another server also works.
 - See the [Charter](charter.md) for how governance is structured.
 - See [Open questions](open-questions.md) for the decisions currently on the table.