_content/doc: add release notes for GOAUTH

For: golang/go#26232
For: golang/go#68545

Change-Id: If5081ffdd69f4c62055180ed80f30b97c3c2126c
Reviewed-on: https://go-review.googlesource.com/c/website/+/634235
Auto-Submit: Sam Thanawalla <samthanawalla@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Michael Matloob <matloob@golang.org>

_content/doc/go1.24.md

@@ -64,6 +64,11 @@ These are distinguished by new `Action` types, but if they cause problems in
 a test integration system, you can revert to the text build output by setting
 `GODEBUG=gotestjsonbuildtext=1`.
 
+<!-- go.dev/issue/26232 -->
+
+The new 'GOAUTH' environment variable provides a flexible way to authenticate
+with private modules. See `go help goauth` for more information.
+
 ### Cgo {#cgo}
 
 <!-- go.dev/issue/56378, CL 579955 -->