[css-writing-modes-3] create non-normative subsection

Author: astearns

css-writing-modes-3/Overview.bs

@@ -692,12 +692,15 @@ Reordering-induced Box Fragmentation</h4>
 <h2 id="vertical-intro">
 Introduction to Vertical Text</h2>
 
-  <p><em>This subsection is non-normative.</em></p>
-
   <p>In addition to extensions to CSS2.1&rsquo;s support for bidirectional text,
     this module introduces the rules and properties needed to support vertical
     text layout in CSS.
 
+<h3 id="vertical-examples">
+Vertical Text Examples</h3>
+
+  <p><em>This section is non-normative.</em></p>
+
   <p>Unlike languages that use the Latin script which are primarily laid out
     horizontally, Asian languages such as Chinese and Japanese can be laid out
     vertically.  The Japanese example below shows the same text laid out