Explicitly list domain and port arguments.

A developer working on a remote server will want to change the IP
address which `npm start` serves on. A developer working on a machine
which is already using port 8000 will want to change the port. By
listing those arguments explicitly, it angular-phonecat makes it easier
for developers who are unfamiliar with npm and are working through the
tutorial to see that they can do so. This should be accompanied by a
scentence in the documentation.