* Update README_docker_io.md
Fix image names in Docker run commands README to include "hashicorp/" prefix to make sure that local trash images will not pollute the process.
* doc: Add trailing backslashes to make it copyable
---------
Co-authored-by: Michael Li <michael.li@hashicorp.com>
This moves the contents of the readme used for hashicorp/boundary on
docker.io/registry.hub.docker.com to a separate readme file from the one that
documents how to build docker images. It also makes some minor fixups
and updates the docker.io readme, must notably updating the minimum
version of postgres that boundary requires.