Auto-download Arial.ttf on init (#4606)

* Auto-download Arial.ttf on init

* Fix ROOT

utils/__init__.py

@@ -0,0 +1,16 @@
+from pathlib import Path
+
+import torch
+from PIL import ImageFont
+
+FILE = Path(__file__).absolute()
+ROOT = FILE.parents[1]  # yolov5/ dir
+
+# Check YOLOv5 Annotator font
+font = 'Arial.ttf'
+try:
+    ImageFont.truetype(font)
+except Exception as e:  # download if missing
+    url = "https://ultralytics.com/assets/" + font
+    print(f'Downloading {url} to {ROOT / font}...')
+    torch.hub.download_url_to_file(url, str(ROOT / font))