Update readme example

[kiramclean]

Updates the example added to the readme to be complete and show the correct example output.

Description

This PR updates the example previously added to the readme in b2e5c1e with the correct output.

Related Issue

• Closes Include minimal pymc example in README #7267
• Related to #

Checklist

• Checked that the pre-commit linting/style checks pass
• Included tests that prove the fix is effective or that the new feature works
• Added necessary documentation (docstrings and/or example notebooks)
• If you are a pro: each commit corresponds to a relevant logical change

Type of change

• New feature / enhancement
• Bug fix
• Documentation
• Maintenance
• Other (please specify):

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📚 Documentation preview 📚: https://pymc--7358.org.readthedocs.build/en/7358/

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