Document using InfluxDB 2 as a systemd service (#2096)

Document using InfluxDB 2 as a systemd service

Also promote "Networking ports" to H3

Co-authored-by: pierwill <pierwill@users.noreply.github.com>
Co-authored-by: Scott Anderson <sanderson@users.noreply.github.com>

content/influxdb/v2.0/get-started.md

@@ -207,7 +207,34 @@ or rename them before putting them in your `$PATH`.
 If you rename the binaries, all references to `influx` and `influxd` in this documentation refer to your renamed binaries.
 {{% /note %}}
 
-#### Networking ports
+### Install InfluxDB as a service with systemd
+
+{{% note %}}
+The following instructions have been tested on Ubuntu, and should work similarly on other Linux distributions.
+{{% /note %}}
+
+1. Download and install the appropriate `.deb` file using a URL from the [InfluxData downloads page](https://portal.influxdata.com/downloads/)
+   with the following commands:
+   ```sh
+   wget https://dl.influxdata.com/influxdb/releases/influxdb2_2.x.x_xxx
+   sudo dpkg -i influxdb2_2.x.x_xxx
+   ```
+   _Use the exact filename of the download of `.deb` package (for example, `influxdb2_2.0.3_amd64.deb`)._
+2. Start the InfluxDB service:
+   ```sh
+   sudo service influxdb start
+   ```
+   Installing the InfluxDB package creates a service file at `/lib/systemd/services/influxdb.service`
+   to start InfluxDB as a background service on startup.
+3. Restart your system and verify that the service is running correctly:
+   ```sh
+   $  sudo service influxdb status
+   ● influxdb.service - InfluxDB is an open-source, distributed, time series database
+     Loaded: loaded (/lib/systemd/system/influxdb.service; enabled; vendor preset: enable>
+     Active: active (running)
+   ```
+
+### Networking ports
 
 By default, InfluxDB uses TCP port `8086` for client-server communication over
 the [InfluxDB HTTP API](/influxdb/v2.0/reference/api/).