Add example config for welcome messages.

mautrix_telegram/example-config.yaml

@@ -394,6 +394,21 @@ bridge:
     # The prefix for commands. Only required in non-management rooms.
     command_prefix: "!tg"
 
+    # Messages sent upon joining a management room.
+    # Markdown is supported. The defaults are listed below.
+    management_room_text:
+        # Sent when joining a room.
+        welcome: "Hello, I'm a Telegram bridge bot."
+        # 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 `login` to log in."
+        # Optional extra text sent when joining a management room.
+        # additional_help: "This would be some additional text in case you need it."
+
+    # Send each message separately (for readability in some clients)
+    management_room_multiple_messages: false
+
     # Permissions for using the bridge.
     # Permitted values:
     #   relaybot - Only use the bridge via the relaybot, no access to commands.