Include yolov5x extra large model weights

weights/download_weights.sh

@@ -4,4 +4,5 @@
 python3 -c "from utils.google_utils import *;
 attempt_download('weights/yolov5s.pt');
 attempt_download('weights/yolov5m.pt');
-attempt_download('weights/yolov5l.pt')"
+attempt_download('weights/yolov5l.pt');
+attempt_download('weights/yolov5x.pt')"