Update README with response file format examples

In vokal-isaac@924cd9071ab202522259a01e8a0182a79efca5c2, I've adjusted the regex so that it fits with our current understanding of what's standard, which means that this should be one blank line:

```
HTTP/1.1 202 Accepted
Content-Type: text/plain; charset=UTF-8
Date: Fri, 17 Oct 2014 14:12:46 GMT
Server: Apache-Coyote/1.1
Content-Length: 0
Connection: keep-alive

<EOF>
```