Display an error message when the TextDecoder interface isn't available.

My intention for this sample was to show the native functionality on supported browsers, so I'm not including the [polyfill](https://github.com/inexorabletash/text-encoding), and just display a message if the browser doesn't support `TextDecoder`.

@ebidel let me know if you think these samples **should** demonstrate use of polyfills (when available).