Update `AutoShape.forward()` model.classes example (#5324)

models/common.py

@@ -277,7 +277,7 @@ class AutoShape(nn.Module):
     # YOLOv5 input-robust model wrapper for passing cv2/np/PIL/torch inputs. Includes preprocessing, inference and NMS
     conf = 0.25  # NMS confidence threshold
     iou = 0.45  # NMS IoU threshold
-    classes = None  # (optional list) filter by class
+    classes = None  # (optional list) filter by class, i.e. = [0, 15, 16] for COCO persons, cats and dogs
     multi_label = False  # NMS multiple labels per box
     max_det = 1000  # maximum number of detections per image