Adding a negative array loop example to the docs

Author: jashkenas

documentation/index.html.erb

@@ -1176,7 +1176,7 @@ Expressions
         </li>
         <li>
           You can now loop over an array backwards, without having to manually
-          deal with the indexes.
+          deal with the indexes: <tt>for item in list by -1</tt>
         </li>
         <li>
           Source locations are now preserved in the CoffeeScript AST, although

index.html

@@ -2346,7 +2346,7 @@ <h2>
         </li>
         <li>
           You can now loop over an array backwards, without having to manually
-          deal with the indexes.
+          deal with the indexes: <tt>for item in list by -1</tt>
         </li>
         <li>
           Source locations are now preserved in the CoffeeScript AST, although