_content/doc/go1.21: mention encoding/binary.NativeEndian

For golang/go#57237
Fixes golang/go#62349

Change-Id: I2407281b1635e3689f6e225da2ea7f562f321203
Reviewed-on: https://go-review.googlesource.com/c/website/+/524675
Reviewed-by: Ian Lance Taylor <iant@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Ian Lance Taylor <iant@google.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>
Auto-Submit: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>

_content/doc/go1.21.html

@@ -725,6 +725,17 @@ <h3 id="minor_library_changes">Minor changes to the library</h3>
   </dd>
 </dl><!-- embed -->
 
+<dl id="encoding/binary"><dt><a href="/pkg/encoding/binary/">encoding/binary</a></dt>
+  <dd>
+    <p><!-- https://go.dev/issue/57237, CL 463218, CL 463985 -->
+      The new
+      <a href="/pkg/encoding/binary/#NativeEndian"><code>NativeEndian</code></a>
+      variable may be used to convert between byte slices and integers
+      using the current machine's native endianness.
+    </p>
+  </dd>
+</dl><!-- encoding/binary -->
+
 <dl id="errors"><dt><a href="/pkg/errors/">errors</a></dt>
   <dd>
     <p><!-- https://go.dev/issue/41198, CL 473935 -->