added a PCEX activity to SLCP demo page

Author: mhassany-pitt

slcp/iframe-protocol-demos.html

@@ -67,6 +67,11 @@ <h2>JS-Parsons</h2>
 </pre> 
       <iframe width='100%' src='https://horstmann.com/private/js-parsons/examples/turtle-test.html'></iframe> 
       <pre class='message'></pre>
+      
+      <h2>PCEX Activity</h2> 
+      <iframe width='100%' src='https://acos.cs.vt.edu/html/acos-pcex/acos-pcex-examples/py_f_to_c_conversion__664e502391363872f0ba38dd'></iframe>
+      <pre class='message'></pre>
+      
       <h2>Add Your Own</h2>
       <p>Enter the address of any element and click the “Add” button. If the element supports the SPLICE iframe protocol, you will see a message whose <code>subject</code> is <code>lti.frameResize</code>. As you interact with the element, watch for <code>SPLICE.reportScoreAndState</code> messages.</p>
       <p>iframe URL: <input id='url' width='50'/> <button id='add'>Add</button></p>