update release notes

Change-Id: If6157c345b0329665ac385de23e42d4cd7331cbc
Docs-Preview: https://skia.org/?cl=376847
TBR Joe
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/376847
Reviewed-by: Heather Miller <hcm@google.com>
Reviewed-by: Joe Gregorio <jcgregorio@google.com>
Commit-Queue: Heather Miller <hcm@google.com>
2 files changed