docs: remove runnerset limitation (#1225)

This works great from testing now, this is no longer a limitation due to ARC now creating a statefulset per runner

Author: toast-gear

README.md

@@ -448,7 +448,6 @@ Under the hood, `RunnerSet` relies on Kubernetes's `StatefulSet` and Mutating We
 **Limitations**
 
 * For autoscaling the `RunnerSet` kind only supports pull driven scaling or the `workflow_job` event for webhook driven scaling.
-* A known down-side of relying on `StatefulSet` is that it misses a support for `maxUnavailable`. A `StatefulSet` basically works like `maxUnavailable: 1` in `Deployment`, which means that it can take down only one pod concurrently while doing a rolling-update of pods. Kubernetes 1.22 doesn't support customizing it yet so probably it takes more releases to arrive. See https://github.com/kubernetes/kubernetes/issues/68397 for more information.
 
 ### Autoscaling