Add systemd service file and related docs (#448)

contrib/beyla@.service

@@ -0,0 +1,17 @@
+[Unit]
+Description=Run the Beyla application for a given application
+After=network.target
+
+[Service]
+Type = simple
+Restart = always
+User = root
+Group = root
+WorkingDirectory = /etc/beyla
+EnvironmentFile = /etc/beyla/%i.env
+ExecStart=
+ExecStart=/usr/local/bin/beyla \
+	--config=/etc/beyla/%i.yaml
+
+[Install]
+WantedBy = multi-user.target

contrib/example-service.env

@@ -0,0 +1 @@
+GRAFANA_CLOUD_API_KEY="<MY-CLOUD-API-KEY>"

contrib/example-service.yaml

@@ -0,0 +1,17 @@
+open_port: 8000
+service_name: my-django-app
+print_traces: true
+
+ebpf:
+  wakeup_len: 100
+
+grafana:
+  otlp:
+    cloud_zone: <my-cloud-zone>
+    cloud_instance_id: <my-instance-id>
+    cloud_submit:
+      - metrics
+      - traces
+routes:
+  unmatched: heuristic
+

docs/sources/setup/standalone.md

@@ -26,6 +26,19 @@ Alternatively, download the Beyla executable with the `go install` command:
 go install github.com/grafana/beyla/cmd/beyla@latest
 ```
 
+## Installing as a service
+
+Once you have Beyla installed on your system, you can use the [systemd service script](https://github.com/grafana/beyla/tree/main/contrib/beyla@.service) to get the daemon up and running.  Installing the script is as simple as creating a file at `/etc/systemd/system/beyla@.service` (the `@` is important!) and running `systemctl daemon-reload`.
+
+The systemd service expects the following requirements to be met:
+
+   * The `beyla` binary is in `/usr/local/bin` and is executable
+   * A directory exists at `/etc/beyla` to hold the various configuration files
+
+The service script works in such a way that it will pick up the files named after the service name that follows the `@` sign.  As an example, if we wanted to use Beyla to monitor a moodle installation, we would create a configuration file at `/etc/beyla/moodle.yaml` and place our environment variables in `/etc/beyla/moodle.env`, then start the service with the command `systemctl start beyla@moodle.service` - the service will automatically pick up the `moodle` related files and start monitoring.
+
+If you want to add a second Beyla install on the same system monitoring a Django installation, you would create `/etc/beyla/django.yaml` and `/etc/beyla/django.env`, then start the service as `systemctl start beyla@django` and it will run alongside the existing Moodle Beyla but with the Django configuration.
+
 ## Configure
 
 Beyla can be configured via: