add noscript hint

src/core/xsl/navbar.xsl

@@ -54,6 +54,7 @@
     </xsl:if>
     <!-- Now the header follows. -->
     <nav class="navbar navbar-default navbar-fixed-top">
+      <noscript>Please enable JavaScript!</noscript>
       <div class="container-fluid">
         <div class="navbar-header">
           <button class="navbar-toggle" data-target="#top-navbar" data-toggle="collapse" type="button">