Adding the in
class on your collapseOne
will make the accordion open by default.
<div id="nav">
<div id="accordion">
<div class="heading"> <a id="about" class="accordion-toggle nav-main-item" data-toggle="collapse" data-parent="#accordion" href="#collapseOne">About</a>
</div>
<!--ends heading-->
<div id="collapseOne" class="collapse">
<ul>
<li><a class="nav-sub-item" href="about.html">me</a>
</li>
<li><a class="nav-sub-item" href="articles.html">articles</a>
</li>
</ul>
</div>
<!--ends collapseOne-->
</div>
</div>
<script>
$(function() {
$('#collapseOne').addClass('in');
});
</script>
Example in JSFiddle