doc: Update virtio network in launch script
Update description of virtio network setting in launch script to match:
@@ -77,7 +77,10 @@ define post-launched User VM settings. This document describes these option sett
``network`` (a child node of ``virtio_devices``):
The virtio network device setting.
- Input format: ``[tap_name|macvtap_name],[vhost],[mac=XX:XX:XX:XX:XX:XX]``.
+ Input format: ``<device_name>,[vhost],[mac=<XX:XX:XX:XX:XX:XX>]``.
+ The ``mac`` address is optional, ``device_name`` is the name of the TAP (or
+ MacVTap) device. It must include the keyword ``tap``. ``vhost`` specifies
+ vhost backend, otherwise the VBSU backend is used.
``block`` (a child node of ``virtio_devices``):
The virtio block device setting.
