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Summary

Add basic pre-commit hooks to the repo. To catch, for example, broken symlinks (WorldHealthOrganization/app#1670)
Link: https://github.com/pre-commit/pre-commit-hooks

Possible config file. Should be run against every file in the existing tree to see what issues might come up.

# .pre-commit-config.yaml
-   repo: https://github.com/pre-commit/pre-comm

🙋 Feature Request

🔦 Context

https://github.com/github/covid19-dashboard/blob/master/_notebooks/2021-04-03-canada-variants-of-concern.ipynb should use the World Health Organization (WHO)'s Greek labels "Alpha", "Beta", "Gamma" instead of "UK", "South Africa", "Brazil", respectively.