#2 Not all audio files are listed in readme

[Matthew Boehm]

Not all the audio files needed to create are listed in the
read me.

These are the ones I found in the source. Only a few are
missing from the readme.

prepaid-auth-fail
prepaid-auth-failed
prepaid-card-expired
prepaid-card-inactive
prepaid-card-in-use
prepaid-dest-blocked
prepaid-dest-unreachable
prepaid-enter-card-num
prepaid-enter-dest
prepaid-invalid-digits
prepaid-no-aaa
prepaid-no-aaatecherror
prepaid-no-card-entered
prepaid-no-cid
prepaid-zero-balance

Can they all be added to the readme to help future
users?