Should mention Account SID must be Live

[kumasento]

Hi,

I tried with the Test Account SID, but there was always a Gateway error. Then I shifted to Live and everything works like a charm.

I think it might be better to mention this in the README.

Thanks

[trnelson]

Agreed. Please make this update to the README file! Otherwise you get a 403 status, 31201 error code (generic error) and an output of "Could not connect to Twilio, undefined..."