Add tooltips to file ordering level options

Closes #7 (closed)

content/js/file_download.js

@@ -23,7 +23,7 @@ var addProducts = function(products,prefix,opt_name){
  */
 
 var product_dict = new Object();
-var addLevels = function(levels,header,prefix){
+var addLevels = function(levels, header, prefix) {
     //keep track of all the products associated with a level's name
     //keep track of all the versions available to the levels
     var versions = new Set();
@@ -36,8 +36,13 @@ var addLevels = function(levels,header,prefix){
         var level_name = level.display_name;
         if(level.display_name == undefined)
             level_name = name.replace('l','L').replace('_',' ');
-        
-        $('#levels').append(makeOption(level_key+' '+header,head_string+level_name,header));
+        var level_desc = level.description;
+        if (level_desc === undefined)
+            level_desc = level_name;
+
+        $('#levels').append(makeOption(
+            level_key + ' ' + header,head_string + level_name,
+            header, level_desc));
         _.each(level.versions,function(version){versions.add(version);});
         product_dict[level_key] = level.products;
     });