Typhon: Nix-based continuous integration

Last weekend, Lucas Franceschino and I officialy announced Typhon!

We presented it at FOSDEM and on the NixOS discourse.

Typhon is a prototype for Nix-based continuous integration, iterating over the concepts of Hydra and introducing actions to replace plugins. It is already running CI for itself (see etna.typhon-ci.org) and we think that it is ready for a public beta. If you are interested in trying it, be sure to check the documentation: after a general introduction it contains instructions to install Typhon and configure a simple GitHub project.