docs(README): fix timezone example code

[psvenk]

ICalCalendar was not imported.

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[sebbo2002]

Thank you for your pull request. 🙏🏼

[sebbo2002]

🎉 This PR is included in version 6.0.1-develop.2 🎉

The release is available on:

• npm package (@next dist-tag)
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• v6.0.1-develop.2

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[sebbo2002]

🎉 This PR is included in version 6.0.1 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release
• v6.0.1

Your semantic-release bot 📦🚀