Documentation issue in Readme.md

[russfellows]

I see that a new container image has been created and pushed to the docker.io container registry. However, the tag used for the latest image is "main" , which is not documented. By default, a pull or push without a tag results in a tag of "latest" being used. There is an image with the latest tag, but it is NOT the latest, and is for 2 year old Arm64 image. The image MOST people will want is now tagged "main", thus the correct pull request would look like "podman/docker pull docker.io/zhenghh04/dlio:main".