Default --data imagenette160 training (fastest) (#9033)

* Default --data `imagenette160` training (fastest)

Signed-off-by: Glenn Jocher <glenn.jocher@ultralytics.com>

* Update train.py

Signed-off-by: Glenn Jocher <glenn.jocher@ultralytics.com>

* Update train.py

Signed-off-by: Glenn Jocher <glenn.jocher@ultralytics.com>

* Update train.py

Signed-off-by: Glenn Jocher <glenn.jocher@ultralytics.com>

Signed-off-by: Glenn Jocher <glenn.jocher@ultralytics.com>

train.py

@@ -436,7 +436,7 @@ def parse_opt(known=False):
     parser.add_argument('--cfg', type=str, default='', help='model.yaml path')
     parser.add_argument('--data', type=str, default=ROOT / 'data/coco128.yaml', help='dataset.yaml path')
     parser.add_argument('--hyp', type=str, default=ROOT / 'data/hyps/hyp.scratch-low.yaml', help='hyperparameters path')
-    parser.add_argument('--epochs', type=int, default=300)
+    parser.add_argument('--epochs', type=int, default=300, help='total training epochs')
     parser.add_argument('--batch-size', type=int, default=16, help='total batch size for all GPUs, -1 for autobatch')
     parser.add_argument('--imgsz', '--img', '--img-size', type=int, default=640, help='train, val image size (pixels)')
     parser.add_argument('--rect', action='store_true', help='rectangular training')