doc/go1.27: document macOS requirements

For golang#75836.

Change-Id: I07f607178fadbfec95459b2a446f58ae3c5e8932
Reviewed-on: https://go-review.googlesource.com/c/go/+/739380
Reviewed-by: Carlos Amedee <carlos@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Dmitri Shuralyov <dmitshur@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>

Author: dmitshur

doc/next/7-ports.md

@@ -1,2 +1,8 @@
 ## Ports {#ports}
 
+### Darwin {#darwin}
+
+<!-- go.dev/issue/75836 -->
+As [announced](go1.26#darwin) in the Go 1.26 release notes,
+Go 1.27 requires macOS 13 Ventura or later;
+support for previous versions has been discontinued.