external perimeter verbose gcode

diff --git a/lib/Slic3r/GCode.pm b/lib/Slic3r/GCode.pm
index 5398be0..9d44f86 100644
--- a/lib/Slic3r/GCode.pm
+++ b/lib/Slic3r/GCode.pm
@@ -303,6 +303,10 @@ sub _extrude_path {
     if ($self->first_layer) {
         $F = $self->config->get_abs_value_over('first_layer_speed', $F/60) * 60;
     }
+
+    if ($path->role == EXTR_ROLE_EXTERNAL_PERIMETER) {
+        $description .= " external";
+    }
     
     # extrude arc or line
     $gcode .= ";_BRIDGE_FAN_START\n" if $path->is_bridge && $self->enable_cooling_markers;