[css-text] Expand on full-size-kana example

Author: frivoal

css-text-3/Overview.bs

@@ -694,6 +694,14 @@ Text Processing</h3>
       in the appropriate places--
       not unlike reading a text in English
       with all “s” characters substituted by “f”.
+
+      For example, if ''text-transform: full-size-kana'' were applied to the following source,
+      the annotation would read “じゆう” (jiyū), which means “liberty”,
+      instead of “じゅう” (jū), which means “ten”,
+      the correct reading and meaning for the annotated “十”.
+      <xmp highlight=html>
+        <ruby>十<rt>じゅう</ruby>
+      </xmp>
     </div>
 
 <h4 id="text-transform-mapping">