Provide systemd files

+ move example cfg from etc/ to cfg/

Change-Id: I437b3e2aaca55539ff110f5a46e411b34e0a0b9c
Reviewed-on: https://forge.frm2.tum.de/review/c/sine2020/secop/playground/+/21319
Tested-by: JenkinsCodeReview <bjoern_pedersen@frm2.tum.de>
Reviewed-by: Enrico Faulhaber <enrico.faulhaber@frm2.tum.de>

etc/secop@.service

@@ -0,0 +1,12 @@
+[Unit]
+Description=SECoP SEC-node: %i
+After=network-online.service
+
+[Service]
+Type=notify
+ExecStart=/usr/bin/secop-server %I
+Restart=on-abnormal
+RestartSec=30
+
+[Install]
+WantedBy=multi-user.target