LICENSE.txt: Add a basic license file

This uses the same licensing as ari-py, which is fairly permissive but does
require that - if you redistribute one of the examples - you state where you
got it from by including this LICENSE information with the source code.
README.md: Add a bit more basic information to the README

This includes the existing tests, with the exception of bridge-infinite-wait.
channel-aa: Add Python example for a simple IVR/automated attendant