ember.js - use of vendor directory

When I try to reference an asset in vendor I get a 404 - would someone tell me what I'm doing wrong ?

In attempting to follow the doco (http://ift.tt/2teOpQA paragraph headed 'Other Assets') I've copied some js/css to the vendor directory.

In index.html I've added :

<script src="vendor/gmaps.js"></script>

When I then run ember s the page is rendered but the references to the assets in vendor return 404.

I've also tried :

 <script src="vendor/gmaps.js"></script>

with the same result.

What am I doing wrong ?