[NixOS] Add git-sync

nixos/configuration.nix

@@ -35,6 +35,40 @@ let
       libappindicator-gtk3
     ];
   });
+  git-sync = with pkgs; stdenv.mkDerivation rec {
+    name = "git-sync-${version}";
+    version = "20151024";
+
+    src = fetchFromGitHub {
+      owner = "simonthum";
+      repo = "git-sync";
+      rev = "eb9adaf2b5fd65aac1e83d6544b9076aae6af5b7";
+      sha256 = "01if8y93wa0mwbkzkzx2v1vqh47zlz4k1dysl6yh5rmppd1psknz";
+    };
+
+    buildInputs = [ makeWrapper ];
+
+    dontBuild = true;
+
+    installPhase = ''
+      mkdir -p $out/bin
+      cp -a git-sync $out/bin/git-sync
+    '';
+
+    wrapperPath = with stdenv.lib; makeBinPath [
+      coreutils
+      git
+      gnugrep
+      gnused
+    ];
+
+    fixupPhase = ''
+      patchShebangs $out/bin
+
+      wrapProgram $out/bin/git-sync \
+        --prefix PATH : "${wrapperPath}"
+      '';
+  };
 in
 {
   nixpkgs.config.allowUnfree = true;
@@ -131,6 +165,7 @@ in
     binutils
     gcc
     gitFull
+    git-sync
     gnumake
     gnupg
     htop