Fix default welcome message

mautrix_signal/example-config.yaml

@@ -214,7 +214,7 @@ bridge:
         # Sent when joining a management room and the user is already logged in.
         welcome_connected: "Use `help` for help."
         # Sent when joining a management room and the user is not logged in.
-        welcome_unconnected: "Use `help` for help or `register` to log in."
+        welcome_unconnected: "Use `help` for help or `link` to log in."
         # Optional extra text sent when joining a management room.
         additional_help: ""