Array index unpacking not supported in Python < 3.11

[lamoreel]

Statements of the form array[*idx] were introduced in Python 3.11. This is used (at least twice: lines 420 and 422) in show.py, resulting in a SyntaxError when using older Python versions.

On a related note, Python 3.8 is no longer supported since last week, so the README must be updated.