_includes/extensions/slideshare.html

<div class="extensions extensions--slide">
  <iframe src="//www.slideshare.net/slideshow/embed_code/key/{{ include.id }}"
    width="595" height="485" frameborder="0" marginwidth="0" marginheight="0" scrolling="no"
    style="border:1px solid #CCC; border-width:1px; margin-bottom:5px; max-width: 100%;" allowfullscreen>
  </iframe>
</div>