docs: bhyve driver documentation improvements

- Document 'domxml-to-native' command
- Mention that the nmdm console support needs an appropriate
  kernel module loaded

docs/drvbhyve.html.in

@@ -98,6 +98,9 @@ the following to the domain XML (<span class="since">Since 1.2.4</span>):
   &lt;/devices&gt;
   ...</pre>
 
+
+<p>Make sure to load the <code>nmdm</code> kernel module if you plan to use that.</p>
+
 <p>
 Then <code>virsh console</code> command can be used to connect to the text console
 of a guest.</p>
@@ -110,6 +113,27 @@ to let a guest boot or start a guest using:</p>
 
 <pre>start --console domname</pre>
 
+<h3><a name="xmltonative">Converting from domain XML to Bhyve args</a></h3>
+
+<p>
+The <code>virsh domxml-to-native</code> command can preview the actual
+<code>bhyve</code> commands that will be executed for a given domain.
+It outputs two lines, the first line is a <code>bhyveload</code> command and
+the second is a <code>bhyve</code> command.
+</p>
+
+<p>Please note that the <code>virsh domxml-to-native</code> doesn't do any
+real actions other than printing the command, for example, it doesn't try to
+find a proper TAP interface and create it, like what is done when starting
+a domain; and always returns <code>tap0</code> for the network interface. So
+if you're going to run these commands manually, most likely you might want to
+tweak them.</p>
+
+<pre>
+# virsh -c "bhyve:///system"  domxml-to-native --format bhyve-argv --xml /path/to/bhyve.xml
+/usr/sbin/bhyveload -m 214 -d /home/user/vm1.img vm1
+/usr/sbin/bhyve -c 2 -m 214 -A -I -H -P -s 0:0,hostbridge -s 3:0,virtio-net,tap0,mac=52:54:00:5d:74:e3 -s 2:0,virtio-blk,/home/user/vm1.img -s 1,lpc -l com1,/dev/nmdm0A vm1
+</pre>
 
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