Update prog.py

>>> prog.py
usage: prog.py [-h] N [N ...]
prog.py: error: too few arguments


>>> prog.py --help
usage: prog.py [-h] N [N ...]

Process some integers.

positional arguments:
  N           a sequence of integers for the program to process

optional arguments:
  -h, --help  show this help message and exit


>>> prog.py 1 2 3
[1, 2, 3]