doc: add doc for required systemd services
"systemd-networkd" is required for acrn-dm to create bridge device.
Document it in GSG before acrn network deb package is ready.
@@ -695,6 +695,14 @@ The ACRN hypervisor boots the Ubuntu Service VM automatically.
[ 0.000000] Hypervisor detected: ACRN
+#. Start the ServiceVM's system daemon for managing network configurations,
+ so the Device Model can create a bridge device that provides User VMs with
+ wired network access:
+
+ .. code-block:: bash
+
+ systemctl enable --now systemd-networkd
+
.. _gsg-user-vm:
.. rst-class:: numbered-step
