Trigger CI workflows on pushes to both main and master + Update PR target branch guideline

[montchr]

Addresses the broken CI workflows mentioned in #369 by allowing workflow triggers on pushes to the master branch since main doesn't exist. This does not necessarily mean #369 can be closed since ideally master will be replaced with main entirely.

[blaggacao]

Thank you a ton! I'll promise to merge any such cleanup PR coming in within the next week within 24 hours.

This is really long overdue and you are doing new folks a great service! (To not to get confused)

[montchr]

Thanks!

I'm gradually working my way through getting up and running with the DevOS template, molding my own configuration into a shape more similar to that of the template with the eventual goal of using the suites/profiles paradigm to compose some NixOS hosts (I haven't yet worked directly with NixOS, only nix-darwin). I hope to provide some more feedback/updates as I progress if I run into other points of confusion that seem like they might be useful to others (rather than the confusion resulting from my own inexperience with NixOS) 😁

I appreciate all the effort all of you have spent on this project 🙂 – it's refreshing to have such a reference point for what can be done with flakes and reusable Nix configurations, even as the template and the API are in flux.