README should replace "poetry shell" with "poetry env activate"

[TheResplandor]

Never used poetry before, but trying to run poetry shell gives me:

$ poetry shell

Looks like you're trying to use a Poetry command that is not available.

Since Poetry (2.0.0), the shell command is not installed by default. You can use,

  - the new env activate command (recommended); or
  - the shell plugin to install the shell command

Documentation: https://python-poetry.org/docs/managing-environments/#activating-the-environment

Note that the env activate command is not a direct replacement for shell command.

The referenced docs seem to recommend using poetry env activate instead. Someone who knows more about poetry should decide if this should be replaced.