Update README.md

[ZoeLeBlanc]

Adding Zenodo badge

Please summarise the reason for your Pull Request here

Checklist

• Assign yourself in the "Assignees" menu
• Add the appropriate "Label"
• If this PR closes an Issue, add the phrase Closes #ISSUENUMBER to your summary above
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• Check the Netlify Preview: navigate to netlify/ph-preview/deploy-preview and click 'details' (at right)
• Assign at least one individual or team to "Reviewers"
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