DevTools: NetworkPanel: show link where resource timing is explained.

Source/devtools/front_end/network/networkPanel.css

 /*
  * Copyright (C) 2006, 2007, 2008 Apple Inc.  All rights reserved.
  * Copyright (C) 2009 Anthony Ricaud <rik@webkit.org>
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *
  * 1.  Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
@@ skipping 92 matching lines @@
 .network-timing-table td {
     padding: 2px 0;
 }
 
 .network-timing-table td.caution {
     font-weight: bold;
     color: rgb(255, 128, 0);
     padding: 2px 0;
 }
 
+.network-timing-table .footnote {
+    border-top: 1px solid #eee;
+}
+
 .network-timing-row {
     position: relative;
     height: 15px;
 }
 
 .network-timing-bar {
     position: absolute;
     min-width: 1px;
     top: 0;
     bottom: 0;
@@ skipping 62 matching lines @@
 
 .request-view.json {
     padding: 5px;
 }
 
 .request-view.html iframe {
     width: 100%;
     height: 100%;
     position: absolute;
 }