Fix XML syntax highlighting

Author: stevepiercy

docs/classic-ui/forms.md

@@ -47,8 +47,8 @@ Here you will find a `configure.zcml` containing the registration of the form.
   class=".my_form.MyForm"
   permission="cmf.ManagePortal"
   layer="p6.theme5.interfaces.IP6Theme5Layer"
-<!-- further ZCML and ZCML footer here  -->
   />
+  <!-- further ZCML and ZCML footer go inside the `browser:page` node  -->
 ```
 
 And a Python file with the code.