Add tooltip on the upload button.

IPython/html/templates/tree.html

@@ -40,7 +40,7 b' data-terminals-available="{{terminals_available}}"'
                 <form id='alternate_upload'  class='alternate_upload'>
                   <span id="notebook_list_info">
                   <span class="btn btn-xs btn-default btn-upload">
-                  <input type="file" name="datafile" class="fileinput" multiple='multiple'>
+                  <input  title="Click to browse for a file to upload." type="file" name="datafile" class="fileinput" multiple='multiple'>
                   Upload
                   </span>
                   </span>