Update voc.yaml

data/voc.yaml

+# PASCAL VOC dataset http://host.robots.ox.ac.uk/pascal/VOC/
+# Download command: bash yolov5/data/get_voc.sh
+# Train command: python train.py --data voc.yaml
+# Dataset should be placed next to yolov5 folder:
+#   /parent_folder
+#     /VOC
+#     /yolov5
 
 # train and val datasets (image directory or *.txt file with image paths)
 train: ../VOC/images/train/
-val: ../VOC/images/val//
+val: ../VOC/images/val/
 
 # number of classes
 nc: 20