Add etesync derivation

nixos/packages/etesync-dav/default.nix

@@ -0,0 +1,18 @@
+with import <nixpkgs> {};
+
+stdenv.mkDerivation rec {
+    name = "etesync-dav";
+    version = "0.5.0";
+    src = fetchurl {
+        url = "https://github.com/etesync/etesync-dav/releases/download/v0.5.0/linux-etesync-dav";
+        sha256 = "0mf7yir1whqbvdfz4551zknanv8wxxk7a21bfgx3lb9kchl6qy9c";
+    };
+
+    unpackCmd = "mkdir unpacked;cp $curSrc ./unpacked/etesync-dav";
+    installPhase = ''
+      mkdir -p $out/bin/
+      cp -vr ./* $out/bin/
+      chmod a+x -R $out/bin/
+    '';
+    buildInputs = [ autoPatchelfHook libzip ];
+}