Add poetry example

[rdmolony]

Description

Adds a poetry example

Motivation and Context

https://github.com/actions/cache/pull/419 was closed as conflicts weren't resolved, I've rebased on main & am happy to close it

How Has This Been Tested?

Are documentation examples tested?

Screenshots (if appropriate):

Types of changes

• [ ] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)
• [x] Documentation (add or update README or docs)

Checklist:

• [ ] My code follows the code style of this project.
• [ ] My change requires a change to the documentation.
• [ ] I have updated the documentation accordingly.
• [ ] I have read the CONTRIBUTING document.
• [ ] I have added tests to cover my changes.
• [ ] All new and existing tests passed.