add flake for game version 10.2.7

flake.nix

@@ -0,0 +1,22 @@
+{
+  description = "Vintagestory";
+
+  inputs = {
+    nixpkgs.url = "github:nixos/nixpkgs?ref=nixos-unstable";
+  };
+
+  outputs = { self, nixpkgs, ... } @ inputs:
+  let
+    system = "x86_64-linux";
+
+    pkgs = import nixpkgs {
+      inherit system;
+
+      config.allowUnfree = true;
+      config.permittedInsecurePackages = [ "dotnet-runtime-7.0.20" ];
+    };
+  in
+  {
+    packages.x86_64-linux.default = pkgs.callPackage ./vintagestory.nix {};
+  };
+}