Intro to co2 data

[lfunderburk]

Describe your changes

Introduction to the CO2 emissions dataset, and the upcoming topics

Issue number

Closes #69

Checklist before requesting a review

• [x] Performed a self-review of my code
• [x] Formatted my code with pkgmt format

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:books: Documentation preview :books:: https://ploomber-sql--74.org.readthedocs.build/en/74/