editorial: remove acknowledgment description

Also adds explanatory comments.

Resolves #525

index.html

@@ -16842,10 +16842,10 @@ <h4>Substantive changes since moving to the Web Application Working Group (forme
     <section class="appendix informative" id="acknowledgements">
       <h3>Acknowledgments</h3>
       <p>The following people contributed to the development of this document.</p>
-      <section class="section" id="ack_group">
-        <h4>Participants active in the HTML Accessibility Task Force active at the time of publication</h4>
+      <section class="section" id="ack_group"> <!-- left in place to ensure deep links to ID remain functional -->
         <ul id="gh-contributors"></ul>
-
+    			<!-- list of contributors will appear here,
+					 along with link to their GitHub profiles -->
         <!--
           TODO:
           Add listing of individuals who have providing meaningful