Add Dockerfile descriptions (#8031)

utils/docker/Dockerfile

 # YOLOv5 🚀 by Ultralytics, GPL-3.0 license
+# Builds ultralytics/yolov5:latest image on DockerHub https://hub.docker.com/r/ultralytics/yolov5
+# Image is CUDA-optimized for YOLOv5 single/multi-GPU training and inference
 
 # Start FROM NVIDIA PyTorch image https://ngc.nvidia.com/catalog/containers/nvidia:pytorch
 FROM nvcr.io/nvidia/pytorch:22.04-py3

utils/docker/Dockerfile-arm64

 # YOLOv5 🚀 by Ultralytics, GPL-3.0 license
-# aarch64-compatible YOLOv5 Docker image for use with Apple M1 and other ARM architectures like Jetson Nano and Raspberry Pi
+# Builds ultralytics/yolov5:latest-arm64 image on DockerHub https://hub.docker.com/r/ultralytics/yolov5
+# Image is aarch64-compatible for Apple M1 and other ARM architectures i.e. Jetson Nano and Raspberry Pi
 
 # Start FROM Ubuntu image https://hub.docker.com/_/ubuntu
 FROM arm64v8/ubuntu:20.04

utils/docker/Dockerfile-cpu

 # YOLOv5 🚀 by Ultralytics, GPL-3.0 license
+# Builds ultralytics/yolov5:latest-cpu image on DockerHub https://hub.docker.com/r/ultralytics/yolov5
+# Image is CPU-optimized for ONNX, OpenVINO and PyTorch YOLOv5 deployments
 
 # Start FROM Ubuntu image https://hub.docker.com/_/ubuntu
 FROM ubuntu:20.04