Update docs/configuring-playbook-prometheus-grafana.md: add two entries for journalctl (matrix-prometheus-node-exporter and matrix-prometheus-postgres-exporter)

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

docs/configuring-playbook-prometheus-grafana.md

@@ -184,6 +184,8 @@ scrape_configs:
 
 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 the commands below:
 - `journalctl -fu matrix-prometheus` for Prometheus
+- `journalctl -fu matrix-prometheus-node-exporter` for Node Exporter
+- `journalctl -fu matrix-prometheus-postgres-exporter` for PostgreSQL Server Exporter
 - `journalctl -fu matrix-grafana` for Grafana
 
 ## More information