docs: Fix copy-paste error in formatdomaincaps

Reported-instead-of-fixing-immediately-by: NJiri Denemark <jdenemar@redhat.com>
Signed-off-by: NMartin Kletzander <mkletzan@redhat.com>
Reviewed-by: NErik Skultety <eskultet@redhat.com>

docs/formatdomaincaps.html.in

@@ -208,7 +208,7 @@
       </dd>
     </dl>
 
-    <h3><a id="elementsIothread">CPU configuration</a></h3>
+    <h3><a id="elementsIothreads">I/O Threads</a></h3>
 
     <p>
       The <code>iothread</code> elements indicates whether or not