Job environment article for self-hosted agents should include a link to docker images

[betelgeuse]

https://docs.semaphoreci.com/ci-cd-environment/job-environment/

"the agent itself can run inside a docker container."

This page should document or point to another page on where the images for the agent are available and any associated instructions for running the images.

It would make sense to have one of options in the Installation article be "Installation using Docker".

https://docs.semaphoreci.com/ci-cd-environment/install-self-hosted-agent/