doc: document GODEBUG options to disable use of instruction set extensions
doc: document GODEBUG options to disable use of instruction set extensions

Fixes #27218

Change-Id: I4eb8e8f2486b20fe0ed6e3e2c6ec521c9e8c0032
Reviewed-on: https://go-review.googlesource.com/c/149579
Reviewed-by: Austin Clements <7ea35d812706d9213868749011af1ed4fa2f6aa0@google.com>

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