Create export files for the african continent

The notebooks on the notebook folders illustrate how the data is organized and exported to CSV files.

The scripts/ecdc.py script fetches up-to-date data from the sources and updates the files on public/data.

The files on this latter directory already have a column indicating the continent, which makes it easy to select only Africa. This issue is about creating a new notebook illustrating how to load the latest data from CSV or JSON in the public/data directory and selecting only the African data. A couple of simple exploratory plots should be added to the notebook for visual inspection of the data. it could be a simple time series plot by country, using plotly.