Add a basic README and stop publishing to Docker Hub #15178

Job	Run time
ubuntu-focal	12s
ubuntu-focal-ros-noetic-ros-core	10s
ubuntu-jammy	10s
ubuntu-noble	12s
ubuntu-focal-ros-noetic-ros-base	8s
ubuntu-focal-ros-noetic-desktop	8s
ubuntu-jammy-ros-humble-ros-core	7s
ubuntu-jammy-ros-humble-ros-base	13s
ubuntu-jammy-ros-humble-desktop	9s
ubuntu-jammy-ros-iron-ros-core	6s
ubuntu-jammy-ros-iron-ros-base	12s
ubuntu-jammy-ros-iron-desktop	12s
build_ubuntu_docker_image_ros	7s
ubuntu-noble-ros-jazzy-ros-base	8s
ubuntu-noble-ros-jazzy-desktop	8s
build_ubuntu_docker_image_ros	10s
ubuntu-noble-ros-rolling-ros-base	11s
ubuntu-noble-ros-rolling-desktop	7s
	2m 50s

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