doc: Add Nix instructions to readme

[siraben]

fq is packaged in Nixpkgs as of NixOS/nixpkgs#151871, so these instructions will work within a few days (once the master channel advances.)

[jtojnar]

That requires Nix flakes enabled.

[siraben]

@jtojnar do you recommend using nix-shell -p fq instead?

[siraben]

Fixed to use stable Nix nix-shell

[wader]

@siraben Thanks, I don't much about nix (but want to know more!) so let me know when and what to do.

[siraben]

@siraben Thanks, I don't much about nix (but want to know more!) so let me know when and what to do.

Sure thing. For the purposes of this PR, like homebrew, Nixpkgs is a monorepo of package definitions, but users use channels, which are essentially points in the repo that have passed all the relevant tests. As such the instructions in this PR wouldn't work right away until the PR has made its way through the channels (see the PR tracker). I'll check periodically until it's green then ping again 😄

Thanks a lot for writing fq by the way!

[wader]

👍 has been a pleasure to write it! hope it's useful and let me know if something seems strange or hard to understand, there are some murky areas in fq that has some accidental design atm.

[siraben]

Rebased on master.

[siraben]

Good to merge now, it's made its way to the unstable channel.

[portothree]

Hey @siraben, sorry for jumping on this after it's already merged, but why are nix-shell -p being used in the section for installation? This is not actually installing the package, it's just spawing a new shell with the jq available there. The user would then need to run nix-shell -p everytime they want to use it.
It should instead be nix-env -iA nixpkgs.fq for non-NixOs and nix-env -iA nixos.fq for NixOS, this will make fq available everywhere in the system. Unless I'm missing something and there's a good reason to use the current command, happy to hear the reasoning.

[siraben]

@portothree generally people in the Nix community want to avoid promoting nix-env (because to new users there can be confusing behavior with nix-env -u among other things), so I followed that convention here. Bringing it in line with the pacman and brew commands is probably fine, though.

[wader]

Hey, i saw that @siraben updated to 0.0.3 in nixpkgs master 👍 but why does nix unstable still say 0.0.2? a bit confused with when things in master gets to unstable

[siraben]

https://nixpk.gs/pr-tracker.html?pr=154449 still not in nixos-unstable yet

[wader]

Aha, thanks for the link, will keep an eye on it, i'm mostly just nix-curious :)

Updates for the -unstable channels typically take a few days after commits land in the master branch.

Now to understand how these builds work.