Determine how to keep DockerHub docs in sync with Tags

[mikeschinkel]

Our wp-cli container's home page says 1.2.1 is the latest yet the tags show 1.5.1. This is not good for us if someone only looks at the main page and not the tags page.

Either we need to move to a fully-automated generation of these Docker main pages or probably better since we can implement sooner we should remove the "Supported tags and respective Dockerfiles" section for the main page and let people look for the tags on the tags page.