Weights download script minor improvements (#5213)

* Add nano model to the download list

* Add possibility to also download the "*6" models

* Cleanup

Co-authored-by: Glenn Jocher <glenn.jocher@ultralytics.com>

data/scripts/download_weights.sh

@@ -11,7 +11,10 @@
 python - <<EOF
 from utils.downloads import attempt_download
 
-for x in ['s', 'm', 'l', 'x']:
+models = ['n', 's', 'm', 'l', 'x']
+models.extend([x + '6' for x in models])  # add P6 models
+
+for x in models:
     attempt_download(f'yolov5{x}.pt')
 
 EOF