Add shell.nix (for local trial-runs of build.sh)

shell.nix

@@ -0,0 +1,24 @@
+/**
+ * This shell is suitable for compiling civix.phar.... and not much else.
+ *
+ * Ex: `nix-shell --run ./build.sh`
+ */
+# { pkgs ? import <nixpkgs> {} }:
+let
+  pkgSrc = fetchTarball {
+    url = "https://github.com/nixos/nixpkgs/archive/ce6aa13369b667ac2542593170993504932eb836.tar.gz";
+    sha256 = "0d643wp3l77hv2pmg2fi7vyxn4rwy0iyr8djcw1h5x72315ck9ik";
+  };
+  pkgs = import pkgSrc {};
+  myphp = pkgs.php74.buildEnv {
+    extraConfig = ''
+      memory_limit=-1
+    '';
+  };
+
+in
+
+  pkgs.mkShell {
+    # nativeBuildInputs is usually what you want -- tools you need to run
+    nativeBuildInputs = [ myphp pkgs.php74Packages.composer ];
+}