Nix: Add support for building using nix

This patch adds a default nix which invokes a `callPackage`
to build sources from the current working directory.

To invoke the build run `nix-build`.

default.nix

@@ -0,0 +1,56 @@
+{ pkgs ? import <nixpkgs> {} }: let
+  package = {
+    rustPlatform,
+    nix-gitignore,
+    pkg-config,
+    openssl,
+    glib,
+    gdk-pixbuf,
+    graphene,
+    cairo,
+    pango,
+    gtk4,
+    libsoup_3,
+    libadwaita,
+    webkitgtk_6_0,
+    libseccomp,
+    wrapGAppsHook4,
+    glib-networking,
+  }: rustPlatform.buildRustPackage {
+    pname = "paket";
+    version = "unstable-2024-08-28";
+
+    src = nix-gitignore.gitignoreSource [] ./.;
+
+    cargoLock.lockFile = ./Cargo.lock;
+
+    nativeBuildInputs = [
+      pkg-config
+      graphene
+      cairo
+      wrapGAppsHook4
+    ];
+
+    buildInputs = [
+      # Building
+      openssl
+      glib
+      gdk-pixbuf
+      pango
+      gtk4
+      libsoup_3
+      libadwaita
+      webkitgtk_6_0 # for JSC
+
+      # Linking
+      libseccomp
+
+      # Runtime
+      glib-networking
+    ];
+
+    meta = {
+      mainProgram = "packet";
+    };
+  };
+in pkgs.callPackage package { }