doc/go1.14: document freebsd/arm64 port
doc/go1.14: document freebsd/arm64 port

Updates #24715

Change-Id: Ie6421cf2d599740bbb0576bcc37bd8ddf5af3961
Reviewed-on: https://go-review.googlesource.com/c/go/+/210119
Reviewed-by: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>

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