fail2ban - add further debugging hint for issue

Signed-off-by: Simon L <szaimen@e.mail.de>

community-containers/fail2ban/readme.md

@@ -4,6 +4,7 @@ This container bundles fail2ban and auto-configures it for you in order to block
 ### Notes
 - This is not working on Docker Desktop since it needs `network_mode: host` in order to work correctly.
 - If you get an error like `"ip6tables v1.8.9 (legacy): can't initialize ip6tables table filter': Table does not exist (do you need to insmod?)"`, you need to enable ip6tables on your host via `sudo modprobe ip6table_filter`.
+- If you get an error like  `stderr: 'iptables: No chain/target/match by that name.'` and `stderr: 'ip6tables: No chain/target/match by that name.'`, you need to follow https://github.com/szaimen/aio-fail2ban/issues/9#issuecomment-2026898790 in order to resolve this.
 - See https://github.com/nextcloud/all-in-one/tree/main/community-containers#community-containers how to add it to the AIO stack
 
 ### Repository