x/website/_content/doc/go1.21: missing encoding.NativeEndian

[ainar-g]

See https://go-review.googlesource.com/c/go/+/463985. It should probably be mentioned in the Minor changes to the library section.

[gopherbot]

Change https://go.dev/cl/524675 mentions this issue: _content/doc/go1.21: mention encoding/binary.NativeEndian