Update setup instructions

Do we want to 'port' https://github.com/datacarpentry/image-processing/pull/342 here? I would think so, since [this change](https://carpentries.org/blog/2025/03/lesson-setup-instructions-task-force-recommendations/) applies to what we are developing here, i.e., a Carpentries lesson in Python.

Start by reviewing the linked image-processing pull request and the Carpentries setup-instructions recommendations, then compare them with this lesson's current setup guidance. Confirm which changes apply to this Python lesson and update the relevant setup instructions; done when the lesson reflects the agreed recommendations.

Written by the indexing model from the issue text.