update Docs regarding Filter-Mode-Flag

docs/configuring-playbook-bridge-mautrix-telegram.md

@@ -59,3 +59,8 @@ matrix_mautrix_telegram_configuration_extension_yaml: |
 
 More details about permissions in this example:
 https://github.com/mautrix/telegram/blob/master/mautrix_telegram/example-config.yaml#L410
+
+If you like to exclude all groups from syncing and use the Telgeram-Bridge only for direct chats, you can add the following additional playbook configuration:
+```yaml
+matrix_mautrix_telegram_filter_mode: whitelist
+```