docs: fix an incorrect example for memoryBacking

commit 136ad497
forgot to add an end-tags for hugepages.
Signed-off-by: NChen Hanxiao <chenhanxiao@cn.fujitsu.com>

docs/formatdomain.html.in

@@ -620,6 +620,7 @@
     <hugepages>
       <page size="1" unit="G" nodeset="0-3,5"/>
       <page size="2" unit="M" nodeset="4"/>
+    </hugepages>
     <nosharepages/>
     <locked/>
   </memoryBacking>