theme.html

<!-- Add the following lines to theme's html code right before </head> -->
<script src="http://ajax.googleapis.com/ajax/libs/jquery/1.7.0/jquery.min.js"></script>
<script src="http://static.tumblr.com/fpifyru/VCxlv9xwi/writecapture.js"></script>
<script src="http://static.tumblr.com/fpifyru/AKFlv9zdu/embedgist.js"></script>

<!--
  Usage: just add <div class="gist">[gist URL]</div>
  Example: <div class="gist">https://gist.github.com/1395926</div>
-->