ci: init, shellcheck job

flake.nix

@@ -0,0 +1,30 @@
+{
+  description = "update-flake-lock";
+
+  inputs.nixpkgs.url = "github:nixos/nixpkgs/nixos-unstable";
+
+  outputs =
+    { self
+    , nixpkgs
+    }:
+    let
+      nameValuePair = name: value: { inherit name value; };
+      genAttrs = names: f: builtins.listToAttrs (map (n: nameValuePair n (f n)) names);
+
+      allSystems = [ "x86_64-linux" "aarch64-linux" "x86_64-darwin" "aarch64-darwin" ];
+      forAllSystems = f: genAttrs allSystems
+        (system: f {
+          inherit system;
+          pkgs = import nixpkgs { inherit system; };
+        });
+    in
+    {
+      devShell = forAllSystems
+        ({ system, pkgs, ... }:
+          pkgs.stdenv.mkDerivation {
+            name = "update-flake-lock-devshell";
+            buildInputs = [ pkgs.shellcheck ];
+            src = self;
+          });
+    };
+}