Major documentation refactor
This tries to fill almost all of the gaps in current runner documentation.
cc @axil @tmaczukin
Fixes https://gitlab.com/gitlab-org/gitlab-ci-multi-runner/issues/994
This tries to fill almost all of the gaps in current runner documentation.
cc @axil @tmaczukin
Fixes https://gitlab.com/gitlab-org/gitlab-ci-multi-runner/issues/994