Add PR#566; something I should have done before.

llvm-svn: 22118

llvm/docs/ReleaseNotes.html

@@ -694,7 +694,7 @@ frontends.</li>
 <div class="doc_text">
 
 <ul>
-  <li>None yet</li>
+<li><a href="http://llvm.cs.uiuc.edu/PR566">Memory Mapped I/O Intrinsics do not fence memory</a></li>
 </ul>
 
 </div>