clarify that sortBy is ascending.

index.html

@@ -521,8 +521,8 @@ <h2 id="collections">Collection Functions (Arrays or Objects)</h2>
       <p id="sortBy">
         <b class="header">sortBy</b><code>_.sortBy(list, iterator, [context])</code>
         <br />
-        Returns a sorted copy of <b>list</b>, ranked by the results of running 
-        each value through <b>iterator</b>.
+        Returns a sorted copy of <b>list</b>, ranked in ascending order by the 
+        results of running each value through <b>iterator</b>.
       </p>
       <pre>
 _.sortBy([1, 2, 3, 4, 5, 6], function(num){ return Math.sin(num); });