Update download_weights.sh comment (#3662)

data/scripts/download_weights.sh

 #!/bin/bash
 # Download latest models from https://github.com/ultralytics/yolov5/releases
 # Usage:
-#    $ bash weights/download_weights.sh
+#    $ bash path/to/download_weights.sh
 
 python - <<EOF
 from utils.google_utils import attempt_download