add default.nix to make the project buildable locally using nix

default.nix

@@ -0,0 +1,46 @@
+# build with: `nix-build`
+# make sure to first checkout the submodules: `git submodule update --init --recursive`
+#
+{ pkgs ? import <nixpkgs> {} }:
+let
+  inherit (pkgs) stdenv;
+in stdenv.mkDerivation {
+  pname = "calls";
+  version = "unstable";
+  src = ./.;
+
+  nativeBuildInputs = with pkgs; [
+    appstream-glib
+    dbus
+    desktop-file-utils
+    docbook-xsl-nons
+    docbook_xml_dtd_43
+    docutils
+    gtk-doc
+    meson
+    ninja
+    pkg-config
+    vala
+    wrapGAppsHook4
+  ];
+
+  buildInputs = with pkgs; [
+    callaudiod
+    evolution-data-server
+    feedbackd
+    folks
+    gom
+    gsound
+    gst_all_1.gst-plugins-bad
+    gst_all_1.gst-plugins-base
+    gst_all_1.gst-plugins-good
+    gst_all_1.gst-plugins-ugly
+    gst_all_1.gstreamer
+    gtk3
+    libadwaita
+    libpeas2
+    libsecret
+    modemmanager
+    sofia_sip
+  ];
+}