Crash on Python <= 3.8

[lucastnr]

Issue

When running main.py with Python <= 3.8 (I'm using 3.8.6), you will receive the following error:

Traceback (most recent call last):
  File "main.py", line 107, in <module>
    def get_version() -> tuple[str, datetime]:
TypeError: 'type' object is not subscriptable

---

I have confirmed that updating Python to 3.9 fixes the issue

Suggestions

1. Update requirements section on README.md to >= 3.9 (Which includes the tuple without importing)
2. Import the tuple in the old-fashioned way.

I will open PRs for each.