doc: add systemd timer and service example

README.md

@@ -26,6 +26,42 @@ Recommended crontab usage:
 
 (do not forget logrotate)
 
+### Systemd
+
+Recommended systemd usage:
+
+```toml
+# /etc/systemd/system/dc-ops.service
+[Unit]
+Description=Run dc-ops once
+After=docker.target
+
+[Service]
+Type=simple
+WorkingDirectory=/opt/dc-ops/
+ExecStart=python3 dc-ops
+```
+
+```toml
+# /etc/systemd/system/dc-ops.timer
+[Unit]
+Description=Start dc-ops service periodically
+
+[Timer]
+Persistent=true
+OnCalendar=*:0/15
+Unit=dc-ops.service
+
+[Install]
+WantedBy=timers.target
+```
+
+Enable and start the timer:
+```
+systemctl enable dc-ops.timer
+systemctl start dc-ops.timer
+```
+
 ## Parameters
 
 See `dc-ops --help`