Fix baseURL documentation in README.md

As far as I can see the `baseURL` is trimmed until the last index of `/`. So in order to achieve the load from `/js/lib/module.js` there is a trailing slash needed.

I have only tested it in the browser.

Author: jansauer

README.md

@@ -85,7 +85,7 @@ All modules are loaded relative to the `baseURL`, which by default is set to the
 We can alter this with:
 
 ```javascript
-  System.baseURL = '/js/lib';
+  System.baseURL = '/js/lib/';
   System.import('module'); // now loads "/js/lib/module.js"
 ```