Added link to (correct) smoke_spec.yaml

Hi, the link to smoke_spec.yaml you have on http://freeside.co/betamax/ in "An example tape file can be found here." is wrong.  I don't know where the src for http://freeside.co/betamax/ is, so instead of just added it to the readme - maybe you want to change http://freeside.co/betamax/ too.

PS: I blogged http://blog2.vorburger.ch/2013/11/rest-api-testing-and-mocking.html yesterday, and (via a friend) found your Betamax today.. ;-) 

PPS: Any thoughts re. the idea to replay a tape against a server? If yes, let's discuss in https://github.com/robfletcher/betamax/issues/119 - @lbovet who just opened it is sitting right opposite me... ;-)