changelog: add entry for GH-258

CHANGELOG.md

@@ -4,6 +4,9 @@ FEATURES:
  * __Datadog APM__: Datadog can be used as an APM source [[GH-241](https://github.com/hashicorp/nomad-autoscaler/pull/241)]
  * __Telemetry__: Initial telemetry implementation to emit key stats for monitoring [[GH-238](https://github.com/hashicorp/nomad-autoscaler/pull/238)]
 
+IMPROVEMENTS:
+ * cluster_scaling: allow Nomad client nodes to be optionally purged after termination [[GH-258](https://github.com/hashicorp/nomad-autoscaler/pull/258)]
+
 BUG FIXES:
  * plugins: fix an issue which caused a failure to launch multiple plugins using the same driver [[GH-222](https://github.com/hashicorp/nomad-autoscaler/issues/222)]
  * policy: fix an issue where the Nomad Autoscaler would fail to canonicalize Nomad APM queries with non-default plugin name [[GH-216](https://github.com/hashicorp/nomad-autoscaler/issues/216)]