Update run-with-systemd.md (#254)

Add documention how to use systemd without root access

docs/administration/run-with-systemd.md

@@ -2,6 +2,7 @@
 
 For non-Docker users, you could run Opengist as a systemd service.
 
+## As root
 On Unix distributions with systemd, place the Opengist binary like:
 
 ```shell
@@ -45,3 +46,47 @@ systemctl daemon-reload
 systemctl enable --now opengist
 systemctl status opengist
 ```
+
+----
+
+## As a normal user
+**NOTE: This was tested on Ubuntu 20.04 and newer. For other distros, please check the respective documentation** 
+
+#### For the purpose of this documentation, we will assume that:
+- You've followed the instructions on how to run opengist [from source](https://github.com/thomiceli/opengist?tab=readme-ov-file#from-source)
+- Your shell user is named `pastebin`
+- All commands are being executed as the `pastebin` user
+
+_If none of the above is true, then adapt the commands and paths to fit your needs._
+
+Enable lingering for the user:
+```shell
+loginctl enable-linger
+```
+
+Create the user systemd folder:
+```
+mkdir -p /home/pastebin/.config/systemd/user
+```
+
+Then create a service file at `/home/pastebin/.config/systemd/user/opengist.service`:
+```ini
+[Unit]
+Description=opengist Server
+After=network.target
+
+[Service]
+Type=simple
+ExecStart=/home/pastebin/opengist/opengist --config /home/pastebin/opengist/config.yml
+Restart=on-failure
+
+[Install]
+WantedBy=default.target
+```
+
+Finally, start the service:
+```shell
+systemctl --user daemon-reload
+systemctl --user enable --now opengist
+systemctl --user status opengist
+```