add astrovim as a nix package

pkgs/astronvim/default.nix

@@ -0,0 +1,30 @@
+{ lib, stdenv, pkgs }:
+
+let
+  user = ./user;
+in
+stdenv.mkDerivation {
+  pname = "astronvim";
+  version = "3.44.1";
+
+  src = pkgs.fetchFromGitHub {
+    owner = "AstroNvim";
+    repo = "AstroNvim";
+    rev = "refs/heads/main";
+    sha256 = "sha256-1nfMx9XaTOfuz1IlvepJdEfrX539RRVN5RXzUR00tfk=";
+  };
+
+  installPhase = ''
+    mkdir $out
+    cp -r * "$out/"
+    mkdir -p "$out/lua/user"
+    cp -r ${user}/* "$out/lua/user/"
+  '';
+
+  meta = with lib; {
+    description = "AstroNvim";
+    homepage = "https://github.com/AstroNvim/AstroNvim";
+    platforms = platforms.all;
+    license = licenses.gpl3;
+  };
+}