Add side margins if screen is too wide

doc/bootstrap/layout.html

@@ -107,7 +107,7 @@
 <div class="container">
   <div class="row">
     {%- block sidebar1 %}{{ bsidebar() }}{% endblock %}
-    <div class="{{ bs_span_prefix }}{{ bs_content_width }}">
+    <div class="col-md-8 col-md-offset-2 content {{ bs_span_prefix }}{{ bs_content_width }}">
       {% block body %}{% endblock %}
     </div>
     {% block sidebar2 %} {# possible location for sidebar #} {% endblock %}