Add files to doc/initial that set up the overall structure
of the release notes document.
For #64169.
Change-Id: Ifbf330e554e1fa20d47c72cc309d5cd26048a323
Reviewed-on: https://go-review.googlesource.com/c/go/+/556817
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>
