Improve docs: contributing, readme, image overview, etc

[shink]

Reference

• https://github.com/docker-library/docs/tree/master/ubuntu
• https://github.com/docker-library/docs/tree/master/spark

[shink]

https://ascend-repo.obs.cn-east-2.myhuaweicloud.com/CANN/CANN%208.0.RC3/Ascend-cann-toolkit_8.0.RC3_linux-x86_64.run?response-content-type=application/octet-stream

https://ascend-repo.obs.cn-east-2.myhuaweicloud.com/CANN/CANN%208.0.RC3/Ascend-cann-toolkit_8.0.RC3_linux-x86_64.run