CHANGELOG.md: add line for Helm v3 upgrade (#2080)

Author: joelanford

CHANGELOG.md

@@ -7,6 +7,7 @@
 ### Changed
 
 - Replace usage of `github.com/operator-framework/operator-sdk/pkg/restmapper.DynamicRESTMapper` with `sigs.k8s.io/controller-runtime/pkg/client/apiutil.DynamicRESTMapper`. ([#2309](https://github.com/operator-framework/operator-sdk/pull/2309))
+- Upgraded Helm operator packages and base image from Helm v2 to Helm v3. Cluster state for pre-existing CRs using Helm v2-based operators will be automatically migrated to Helm v3's new release storage format, and existing releases may be upgraded due to changes in Helm v3's label injection. ([#2080](https://github.com/operator-framework/operator-sdk/pull/2080))
 
 ### Deprecated