Clarify User Import Instructions

This commit updates the instructions for User imports letting the Agent know they should type 'Name, Email' on the first line and then put each new User Name/Email on the following lines to import Users.

include/staff/templates/user-import.tmpl.php

@@ -34,7 +34,7 @@ if ($org_id) { ?>
 'To import more other fields, use the Upload tab.'); ?></em>
 </p>
 <textarea name="pasted" style="display:block;width:100%;height:8em"
-    placeholder="<?php echo __('e.g. John Doe, john.doe@osticket.com'); ?>">
+    placeholder="<?php echo __('Name, Email'. PHP_EOL. ' John Doe, john.doe@osticket.com'); ?>">
 <?php echo $info['pasted']; ?>
 </textarea>
 </div>