Update docker.md as per #1035
What does this MR do?
This MR fix a snippet that shows how to start a runner. The socket volume mount is missing, as pointed in #1035 (closed), so we couldn't get our runners to work.
This MR fix a snippet that shows how to start a runner. The socket volume mount is missing, as pointed in #1035 (closed), so we couldn't get our runners to work.