added documentation re #585810 - restore the vhost conf of a site on rollback from failed migration

platform/migrate.provision.inc

@@ -36,6 +36,7 @@ function drush_provision_drupal_pre_provision_migrate($url, $platform) {
 
 /**
  * Remove the extracted site directory
+ * Restore the vhost conf per the original platform
  */
 function drush_provision_drupal_pre_provision_migrate_rollback($url, $platform) {
   $success =  provision_path("unlink", drush_get_option('backup_file'), TRUE, dt('Removed unused migration site package'), dt('Could not remove unused migration site package'));