Create help command for /runners chatops command
## Overview
We have chatops command called `/runners` to [deploy the ci-runners service](https://gitlab.com/gitlab-com/runbooks/-/blob/master/docs/ci-runners/linux/blue-green-deployment.md), and this also provides some extra [commands](https://gitlab.com/gitlab-com/gl-infra/ci-runners/deployer/-/blob/3b6a9b58577d85510d327c8c948d39e2def03b86/.gitlab-ci.yml#L77-87). It's not very discoverable what commands are available and what they do.
Providing a `/runners help` or by default print the help information like other Linux based CLIs might be helpful for discoverability.
issue