add M86 branch release notes

Bug: skia:
Change-Id: I62331cab6cfadbaf9ab2f74e316cb7a2515249d0
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/312305
Reviewed-by: Joe Gregorio <jcgregorio@google.com>
Reviewed-by: Heather Miller <hcm@google.com>
Commit-Queue: Heather Miller <hcm@google.com>
2 files changed