Add note to runner autoscaling for runner manager on preemptive mode
What does this MR do?
Add note to runner autoscaling on idle_count
configuration and preemptive mode.
Why was this MR needed?
We are updating the Runner Autoscaling docs as needed to incorporate customer feedback raised on the GitLab Runner Autoscaling - Feedback issue
gitlab#408131 (comment 1377369070)