Make the ruby section less HTML specific (2)

This PR applies Fuqiao's PR at #39 to the newly refactored markup.

index.html

@@ -2325,7 +2325,7 @@ <h3>Ruby text annotations</h3>
 	</div>
 
    	<div class="req" id="ruby_rb">
-	<p class="advisement">Ruby implementations should make it possible to use an explicit <code class="kw" translate="no">rb</code> tag for ruby bases.</p>
+	<p class="advisement">Ruby implementations should make it possible to use an explicit element for ruby bases, like the <code class="kw" translate="no">rb</code> element in HTML.</p>
 	</div>
 
    	<div class="req" id="ruby_dblsided">