added: hydra job

flake.nix

@@ -21,6 +21,7 @@
             buildInputs = [ cargo rustfmt nettle llvmPackages_10.clang llvmPackages_10.libclang pkgconfig ];
             LIBCLANG_PATH = "${llvmPackages_10.libclang}/lib";
           };
+          hydraJobs.build = defaultPackage;
         }
       ) // rec {
       nixosModules.brownpaper = import ./mod.nix;