Add Rivr Analytics to download page (#1) (#1032)

Author: AlessandroDG

download.md

@@ -358,6 +358,13 @@ Note: If you receive an error during download you most likely selected a configu
   </div>
 </div>
 
+<div class="col-md-4">
+  <div class="checkbox">
+    <label>
+      <input type="checkbox" analyticscode="rivr" class="analytics-check-box" /> Rivr Analytics
+    </label>
+  </div>
+</div>
 
 </div>
 <br/>