i18n: Add context for "Agent Maximum File Size"

include/staff/settings-tickets.inc.php

@@ -231,7 +231,9 @@ if(!($maxfileuploads=ini_get('max_file_uploads')))
             </td>
         </tr>
         <tr>
-            <td width="180"><?php echo __('Agent Maximum File Size');?>:</td>
+            <td width="180"><?php echo __(
+                // Maximum size for agent-uploaded files (via SCP)
+                'Agent Maximum File Size');?>:</td>
             <td>
                 <select name="max_file_size">
                     <option value="262144">&mdash; <?php echo __('Small'); ?> &mdash;</option>