add ruby variant example

Author: John Daggett

css3-fonts/Fonts.html

@@ -3916,11 +3916,15 @@ <h3 id=font-variant-alternates-prop><span class=secno>6.8 </span>Alternates
   <dl>
    <dt><dfn id=ruby>ruby</dfn>
 
-   <dd>Enables display of ruby glyphs (OpenType feature: <code>ruby</code>).
-    This value only selects a glyph for use in ruby text, it does not affect
-    font scaling.
+   <dd>Enables display of ruby variant glyphs (OpenType feature:
+    <code>ruby</code>). This value only selects a glyph for use in ruby text,
+    it does not affect font scaling. The red ruby text below is shown with
+    default glyphs (top) and with ruby variant glyphs (bottom). Note the
+    slight difference in stroke thickness.
   </dl>
 
+  <div class=featex><img alt="ruby variant example" src=rubyshinkansen.png></div>
+
   <h3 id=font-feature-values><span class=secno>6.9 </span>Defining font
    specific alternates: the @font-feature-values rule</h3>