add link to file server (#1367)

sd-card/html/graph.html

@@ -30,6 +30,8 @@
             <option value="5">Change-Rate</option>
             <option value="6">Change-Absolut</option>
         </select>
+        
+        &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href=fileserver/log/data/>Download</a>
 
   <!-- <button onclick="document.getElementById('editor').hidden = false; this.hidden = true;" >Editor</button> -->
     <div id='editor' hidden='true'>