docs: update news file

with info about support for using precreated tap/macvtap devices in
unprivileged libvirtd.
Signed-off-by: NLaine Stump <laine@redhat.com>

docs/news.xml

@@ -206,6 +206,21 @@
     </section>
   </release>
   <release version="v5.8.0" date="2019-10-05">
+    <section title="New features">
+      <change>
+        <summary>
+          qemu: Support use of precreated tap/macvtap devices by unprivileged libvirtd
+        </summary>
+        <description>
+          It is now possible for an unprivileged libvirtd to make use
+          of tap and macvtap devices that were previously created by
+          some other entity. This is done by setting
+          <code>managed='no'</code> along with the device name in the
+          <code>target</code> subelement of <code>&lt;interface
+          type='ethernet'&gt;</code>.
+        </description>
+      </change>
+    </section>
     <section title="Removed features">
       <change>
         <summary>