You don't need it.
This commit supercedes
<https://github.com/mitchellh/zig-overlay/pull/60>,
which copies a function from `flake-utils`.
Instead of using this (arguably bad) abstraction,
introduce `eachSystem` and `pkgsFor`.
This is the best practice for Flakes or clients of nixpkgs in general.
The `release-<YY.MM>` branch is actually a dev branch:
Hydra continually tests the tip of this branch.
When the tests succeed, the `nixos-<YY.MM>` release branch is updated to
point to the succeeding commit.
`release-<YY.MM>` is to `nixos-<YY.MM>` what `master` is to `nixpkgs-unstable`.
See also: e88fb997e3/CONTRIBUTING.md (flow-of-merged-pull-requests)
