add mention of classes to use for button sizes

docs/base-css.html

@@ -1262,7 +1262,7 @@ For example, <code>section</code> should be wrapped as inline.
   <div class="row">
     <div class="span4">
       <h3>Multiple sizes</h3>
-      <p>Fancy larger or smaller buttons? Have at it!</p>
+      <p>Fancy larger or smaller buttons? Add <code>.btn-large</code> or <code>.btn-small</code> for two additional sizes.</p>
       <p>
         <a href="#" class="btn btn-large btn-primary">Primary action</a>
         <a href="#" class="btn btn-large">Action</a>

docs/templates/pages/base-css.mustache

@@ -1186,7 +1186,7 @@
   <div class="row">
     <div class="span4">
       <h3>{{_i}}Multiple sizes{{/i}}</h3>
-      <p>{{_i}}Fancy larger or smaller buttons? Have at it!{{/i}}</p>
+      <p>{{_i}}Fancy larger or smaller buttons? Add <code>.btn-large</code> or <code>.btn-small</code> for two additional sizes.{{/i}}</p>
       <p>
         <a href="#" class="btn btn-large btn-primary">{{_i}}Primary action{{/i}}</a>
         <a href="#" class="btn btn-large">{{_i}}Action{{/i}}</a>