feat(nix): add package for the project

.gitignore

@@ -1,2 +1,3 @@
 /.direnv
 /target
+/result

flake.nix

@@ -11,10 +11,17 @@
     flake-utils.lib.eachDefaultSystem
     (system: let
       pkgs = import nixpkgs {inherit system;};
+      pname = "osdb";
+      version = "0.1.0";
     in
       with pkgs; {
         devShells.default = mkShell {
           buildInputs = [pkgs.cargo];
         };
+        packages.default = pkgs.rustPlatform.buildRustPackage {
+          src = ./.;
+          cargoLock.lockFile = ./Cargo.lock;
+          inherit pname version;
+        };
       });
 }