fix part of #13111: hide the docs nav on small and below devices

docs/_layouts/default.html

@@ -26,7 +26,7 @@
           {{ content }}
         </div>
         <div class="col-md-3">
-          <div class="bs-docs-sidebar hidden-print" role="complementary">
+          <div class="bs-docs-sidebar hidden-print hidden-xs hidden-sm" role="complementary">
             <ul class="nav bs-docs-sidenav">
               {% if page.slug == "getting-started" %}
                 {% include nav/getting-started.html %}