Add flake package export

flake.nix

@@ -27,6 +27,17 @@
             ];
             env = { };
           };
+
+          packages.wl-backdrop =
+            let
+              cargoToml = fromTOML (builtins.readFile ./Cargo.toml);
+            in
+            pkgs.rustPlatform.buildRustPackage {
+              inherit (cargoToml.package) name version;
+              src = ./.;
+              cargoLock.lockFile = ./Cargo.lock;
+              env = { };
+            };
         };
 
       flake = {