runtime: add available godoc link

runtime: add available godoc link

Change-Id: Ifb4844efddcb0369b0302eeab72394eeaf5c8072
Reviewed-on: https://go-review.googlesource.com/c/go/+/540022
Reviewed-by: Michael Knyszek <mknyszek@google.com>
Auto-Submit: Michael Knyszek <mknyszek@google.com>
Reviewed-by: Heschi Kreinick <heschi@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: shuang cui <imcusg@gmail.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>