updated reference page. closes 284

Author: the-alex

reference.html

@@ -6,13 +6,8 @@ <h1>Quick Reference</h1>
 
 <p>This page collects commands we have (or will) discuss throughout the course.
 Click on a command for more details on its operation and some examples of
-common or useful operations.</p>
-
-<div class="alert alert-warning">
-  <span class="glyphicon glyphicon-warning-sign"></span>
-  This page is under construction. If you would like to help out, check out
-  <a href="/static/f16/advanced/c4cs-wk7-advanced.pdf">Week 7&rsquo;s Advanced Homework</a>.
-</div>
+common or useful operations. We encourage students to contribute to this page
+through the advanced homework on git and open source contributions.</p>
 
 {% for category in site.command_categories %}
   <h2><a class="anchor" name="{{category}}"></a>{{ category | capitalize }}</h2>