doc: document Go 1.12.12
doc: document Go 1.12.12

Change-Id: I832ba5f32d513b586bb0b02371231786b25631e3
Reviewed-on: https://go-review.googlesource.com/c/go/+/201817
Reviewed-by: Andrew Bonventre <682ad9f487f614f19e8b7cc5d340bdc8e1c1b128@golang.org>

nawawi/go,cloudflare/go,CAFxX/go,akutz/go,akutz/go,cloudflare/go,akutz/go,nawawi/go,nawawi/go,CAFxX/go,CAFxX/go,CAFxX/go,golang/go,cloudflare/go,golang/go,CAFxX/go,nawawi/go,akutz/go,cloudflare/go,cloudflare/go,cloudflare/go,cloudflare/go,golang/go,CAFxX/go,CAFxX/go,golang/go,nawawi/go,cloudflare/go,akutz/go,CAFxX/go,akutz/go,golang/go,nawawi/go,nawawi/go,akutz/go,golang/go,akutz/go,golang/go,nawawi/go,golang/go