Feature request: add official Cachix.org

[tromshusky]

Hey, how about adding a github action for cachix.org?
It would provide build caches, so users wouldnt have to compile the project self.

i could write a PR with the gh-action and a how-to in the Readme to add the substituter to the configuration.nix

it would come down to the repo maintainers to add a Cachix token to the repo secrets, or better creating an account self (for full 5GB free tier).
I'd like to try to add aarch64 cross-compiling too, since i use nsc on a pinetab2.