news: add description about downscript

Signed-off-by: NChen Hanxiao <chen_han_xiao@126.com>
Reviewed-by: NMichal Privoznik <mprivozn@redhat.com>

docs/news.xml

@@ -52,6 +52,16 @@
   </release>
   <release version="v6.3.0" date="2020-05-05">
     <section title="New features">
+      <change>
+        <summary>
+          qemu: support network interface downscript
+        </summary>
+        <description>
+          QEMU has the ability to run a script when a NIC is brought up
+          and down. Libvirt only enables use of the up script.
+          Now add support for postscript when NIC is down/detached.
+        </description>
+      </change>
       <change>
         <summary>
           qemu: support disabling hotplug/unplug of PCIe devices