_content/doc/go1.26: expand SIMD release notes

Mention that a high-level portable package is planned.

Also add a very brief overview/example of the API.

Change-Id: Ia9aa9e5890637224da6fab71c7267a8a9cf327ed
Reviewed-on: https://go-review.googlesource.com/c/website/+/733260
Reviewed-by: David Chase <drchase@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

_content/doc/go1.26.md

diff --git a/_content/doc/go1.26.md b/_content/doc/go1.26.md
index c75e6c4..7de902e 100644
--- a/_content/doc/go1.26.md
+++ b/_content/doc/go1.26.md
@@ -269,9 +269,18 @@
 `GOEXPERIMENT=simd` at build time.
 This package provides access to architecture-specific SIMD operations.
 It is currently available on the AMD64 architecture, supporting
-128-bit, 256-bit, and 512-bit vectors.
+128-bit, 256-bit, and 512-bit vector types, such as
+[`Int8x16`](/pkg/simd/archsimd#Int8x16) and
+[`Float64x8`](/pkg/simd/archsimd#Float64x8), with operations such as
+[`Int8x16.Add`](/pkg/simd/archsimd#Int8x16.Add).
 
-See the [proposal issue](/issue/73787) for more details.
+This package is architecture-specific, and the API may not be portable
+across all architectures.
+Building on top of this, we plan to develop a high-level portable SIMD
+package in the future.
+
+See the package documentation and the [proposal issue](/issue/73787)
+for more details.
 
 ### New experimental runtime/secret package