Adds description with KB link

assets/js/src/subscribers/importExport/export.js

@@ -109,7 +109,7 @@ define(
        'first_name',
        'last_name',
        'list_status',
-       'global_status',
+       'global_status'
      ]).trigger('change');
 
      nextStepButton.click(function nextClick() {

views/subscribers/importExport/export.html

@@ -37,6 +37,12 @@
       <th scope="row">
         <label for="export_columns">
           <%= __('List of fields to export') %>
+          <p class="description">
+            <%= __('<strong>[link]Read the guide on the fields.[/link]')
+            |replaceLinkTags('http://beta.docs.mailpoet.com/article/XXX', {'target' : '_blank'})
+            |raw
+            %>
+          </p>
         </label>
       </th>
       <td>