Automate metrics timeline update

We should find a way to automate somehow the metrics pipeline update.

https://pulse.internetsociety.org/shutdowns has an api with events. We could query it once a week and import it in our timeline.

This could be the first external source and we could add more sources as we see fit.

With this, we should move the current timeline out of the README and into a format that is easy to parse for a computer program.