add the first version of the baremetal systemd configuration

Setup-bitwarden_rs-as-a-systemd-service-(autostart).md

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+Making bitwarden_rs start on system startup and use the other facilities of systemd (e.g. isolation, logging,...) requires a `.service` file. The following is a usable starting point:
+```
+[Unit]
+Description=Bitwarden Server (Rust Edition)
+Documentation=https://github.com/dani-garcia/bitwarden_rs
+After=network.target
+
+[Service]
+# The user/group bitwarden_rs is run under. the working directory (see below) should allow write and read access to this user/group
+User=bitwarden_rs
+Group=bitwarden_rs
+# The location of the .env file for configuration
+EnvironmentFile=/etc/bitwarden_rs.env
+# The location of the compiled binary
+ExecStart=/usr/bin/bitwarden_rs
+# Set reasonable connection and process limits
+LimitNOFILE=1048576
+LimitNPROC=64
+# Isolate bitwarden_rs from the rest of the system
+PrivateTmp=true
+PrivateDevices=true
+ProtectHome=true
+ProtectSystem=strict
+# Only allow writes to the following directory and set it to the working directory (user and password data are stored here)
+WorkingDirectory=/var/lib/bitwarden_rs
+ReadWriteDirectories=/var/lib/bitwarden_rs
+# Allow bitwarden_rs to bind ports in the range of 0-1024
+AmbientCapabilities=CAP_NET_BIND_SERVICE
+
+[Install]
+WantedBy=multi-user.target
+```
+Change all paths to match your installation (`WorkingDirectory` and `ReadWriteDirectory` should be the same),
+name this file `bitwarden_rs.service` and put it into `/etc/systemd/system` .
+To make systemd aware of it, run
+```
+$ sudo systemctl daemon-reload
+```
+
+To start this new "service", run
+```
+$ sudo systemctl start bitwarden_rs.service
+```
+
+To enable autostart, run
+```
+$ sudo systemctl enable bitwarden_rs.service
+```
+In the same way you can `stop`, `restart` and `disable` the service.
+If you want to see the logging output, run
+```
+$ journalctl -u bitwarden_rs.service
+```
+or to see a more concise state of the service, run
+```
+$ systemctl status bitwarden_rs.service
+```
+
+For more information on .service files, see the manpages of [systemd.service](https://www.freedesktop.org/software/systemd/man/systemd.service.html) and (for the security configuration) [systemd.exec](https://www.freedesktop.org/software/systemd/man/systemd.exec.html)