Matrix docs: note Element X apps are not currently supported (legacy SSO)

getting-started.md

@@ -67,6 +67,10 @@ privacy, and direction happen on our **Loomio forum**:
   - **Element** (web, desktop, iOS, Android): on the sign-in screen, click *Edit* next to
     "Homeserver" and enter `https://matrix.inference.coop`, then sign in with your co-op
     account. (On [app.element.io](https://app.element.io) or the desktop/mobile apps alike.)
+    **Note:** the new **Element X** apps (iOS/Android/macOS) are *not* currently supported —
+    they only work with the newer Matrix Authentication Service, which this server doesn't
+    run yet. Use the classic Element apps (Element Web / Element Desktop / "Element" on the
+    app stores) or another client below.
   - **FluffyChat, Cinny, SchildiChat** or any other client: look for the "custom homeserver"
     / "other server" option in the client's login screen and enter the same address.
   - Your co-op account and your existing Matrix account on another server (e.g.