Update dataset headers (#4162)

data/coco128.yaml

@@ -1,9 +1,10 @@
-# COCO 2017 dataset http://cocodataset.org - first 128 training images
-# Train command: python train.py --data coco128.yaml
-# Default dataset location is next to YOLOv5:
-#   /parent
-#     /datasets/coco128
-#     /yolov5
+# Copyright Ultralytics https://ultralytics.com, licensed under GNU GPL v3.0
+# COCO128 dataset https://www.kaggle.com/ultralytics/coco128 (first 128 images from COCO train2017)
+# YOLOv5 🚀 example usage: python train.py --data coco128.yaml
+# parent
+# ├── yolov5
+# └── datasets
+#     └── coco128  ← downloads here
 
 
 # Train/val/test sets as 1) dir: path/to/imgs, 2) file: path/to/imgs.txt, or 3) list: [path/to/imgs1, path/to/imgs2, ..]