Maybe something more discreet than a large button at the beginning, like:

  <p>(Code samples are hidden. <label><input type="checkbox" id="showCodeSamples"/> Show code samples</label>)</p>

As a note of feedback, I didn't notice the button at all. (Only knowing about its existence after looking at HN comments.) You do need to take a little bit a the viewer's attention for them to know about the feature.