update release notes file, site for 84 branch

Bug: skia:
Change-Id: Icdc056e7972cad814fa633b7c9b021f4534d60c9
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/290119
Reviewed-by: Joe Gregorio <jcgregorio@google.com>
Commit-Queue: Heather Miller <hcm@google.com>
2 files changed