add note to docs about Respond.js & file:// ; fixes part of #11019

getting-started.html

@@ -176,7 +176,8 @@ bootstrap/
     <!-- Bootstrap -->
     <link href="css/bootstrap.min.css" rel="stylesheet" media="screen">
 
-    <!-- HTML5 shim and Respond.js IE8 support of HTML5 elements and media queries -->
+    <!-- HTML5 Shim and Respond.js IE8 support of HTML5 elements and media queries -->
+    <!-- WARNING: Respond.js doesn't work if you view the page via file:// -->
     <!--[if lt IE 9]>
       <script src="https://oss.maxcdn.com/libs/html5shiv/3.6.2/html5shiv.js"></script>
       <script src="https://oss.maxcdn.com/libs/respond.js/1.3.0/respond.min.js"></script>
@@ -773,6 +774,10 @@ bootstrap/
       <h4>Respond.js and cross-domain CSS</h4>
       <p>Using Respond.js with CSS hosted on a different (sub)domain (for example, on a CDN) requires some additional setup. <a href="https://github.com/scottjehl/Respond/blob/master/README.md#cdnx-domain-setup">See the Respond.js docs</a> for details.</p>
     </div>
+    <div class="bs-callout bs-callout-warning" id="respond-file-proto">
+      <h4>Respond.js and <code>file://</code></h4>
+      <p>Due to browser security rules, Respond.js doesn't work with pages viewed via the <code>file://</code> protocol (like when opening a local HTML file). To test responsive features in IE8, view your pages over HTTP(S). <a href="https://github.com/scottjehl/Respond/blob/master/README.md#support--caveats">See the Respond.js docs</a> for details.</p>
+    </div>
     <div class="table-responsive">
       <table class="table table-bordered table-striped">
         <thead>