cmd/cgo: use doc link for cgo.Handle
Change-Id: If6af9842f563fe9233de0563d356e925a7b912f8
GitHub-Last-Rev:
e8422e9a5aa9ca3140c96f7abfa4fa4482d709ab
GitHub-Pull-Request: golang/go#76727
Reviewed-on: https://go-review.googlesource.com/c/go/+/727581
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: David Chase <drchase@google.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Sean Liao <sean@liao.dev>
Auto-Submit: Sean Liao <sean@liao.dev>