Update docs/configuring-playbook-alertmanager-receiver.md: add the common section "Troubleshooting"

The configuration was copied from main.yml.

Signed-off-by: Suguru Hirahara <acioustick@noreply.codeberg.org>

docs/configuring-playbook-alertmanager-receiver.md

@@ -130,3 +130,16 @@ route:
 ```
 
 where `URL_HERE` looks like `https://matrix.example.com/matrix-alertmanager-receiver-RANDOM_VALUE_HERE/alert/some-room-name` or `https://matrix.example.com/matrix-alertmanager-receiver-RANDOM_VALUE_HERE/alert/!qporfwt:example.com`.
+
+## Troubleshooting
+
+As with all other services, you can find the logs in [systemd-journald](https://www.freedesktop.org/software/systemd/man/systemd-journald.service.html) by logging in to the server with SSH and running `journalctl -fu matrix-alertmanager-receiver`.
+
+### Increase logging verbosity
+
+The default logging level for this component is `info`. If you want to increase the verbosity, add the following configuration to your `vars.yml` file and re-run the playbook:
+
+```yaml
+# Valid values: error, warn, info, debug
+matrix_alertmanager_receiver_container_process_argument_log_level: debug
+```