chore: add nix

nix/shell.nix

@@ -0,0 +1,31 @@
+{ pkgs, rustToolchain }:
+pkgs.mkShell {
+  name = "cosmic-greeter-devshell";
+  packages = builtins.attrValues {
+    inherit
+      rustToolchain
+      ;
+    inherit (pkgs)
+      rust-analyzer-unwrapped
+      nixd
+      libxkbcommon
+      dav1d
+      libinput
+      linux-pam
+      gcc
+      glibc
+      cmake
+      ;
+    inherit (pkgs.llvmPackages)
+      libclang
+      llvm
+      ;
+  };
+
+  nativeBuildInputs = [ pkgs.pkg-config ];
+
+  RUST_SRC_PATH = "${rustToolchain}/lib/rustlib/src/rust/library";
+  LLVM_CONFIG_PATH = "${pkgs.llvmPackages.llvm}/bin/llvm-config";
+  LIBCLANG_PATH = "${pkgs.llvmPackages.libclang.lib}/lib";
+  BINDGEN_EXTRA_CLANG_ARGS = "-I${pkgs.linux-pam}/include -I${pkgs.glibc.dev}/include";
+}