Update the documentation for the tethering

Hey,
After a discussion on discord I've find out how to do tethering with OpenHD, the documentation is not that verbose so I've enhanced it a little bit to give an average user to have video on the RPI (for example send it to goggles as I do) and raw video on the laptop for some advanced stuff (flying with waypoint in qground and having video).
It works like a charm!

software-setup/ethernet-hotspot.md

@@ -15,6 +15,25 @@ In Passive mode, OpenHD's Ethernet is configured as a client, allowing you to co
 2. Wait briefly.
 3. Open a terminal and enter the command: `sudo arp-scan --interface=eth0 --localnet` (**Replace ETH0 with the correct adapter connected to the SBC**).
 4. Test the connection by entering the SBC's IP address into your web browser; it should redirect you to the OpenHD web interface.
+### Tethering
+
+1. **Record IP Addresses:**  
+   Once connected, note the IP addresses of both devices:
+   - **SBC IP**: For example, `10.42.0.118`
+   - **Laptop IP**: For example, `10.42.0.1`
+
+2. **Configure Forwarding in OpenHD:**  
+   SSH into the RPI (user and password is `openhd`).Open the `hardware.conf` file located in `/boot/openhd/` on your SBC. Modify the `NW_MANUAL_FORWARDING_IPS` IP address to point to your laptop’s IP:
+
+   ```bash
+   # Specify additional IP address(es) for video and telemetry forwarding.
+   # OpenHD can detect external devices based on the connection and platform.
+   # Only applicable on ground units.
+
+   NW_MANUAL_FORWARDING_IPS = 10.42.0.1  # Replace with your Ground Station IP (laptop)
+   ```
+
+This setup will ensure that video and telemetry data are directed to your laptop's IP, enhancing your tethered OpenHD experience.
 
 ### Setup on Windows