butler: init at 15.21.0

It's not confirmed to be working though yet... I'm just packaging it for
the sake of packaging it. XD

pkgs/butler.nix

@@ -0,0 +1,26 @@
+{ stdenv, lib, buildGoModule, fetchFromGitHub, brotli, p7zip }:
+
+buildGoModule rec {
+  pname = "butler";
+  version = "15.21.0";
+
+  src = fetchFromGitHub {
+    owner = "itchio";
+    repo = pname;
+    rev = "v${version}";
+    sha256 = "sha256-vciSmXR3wI3KcnC+Uz36AgI/WUfztA05MJv1InuOjJM=";
+  };
+
+  vendorSha256 = "sha256-vdMu4Q/1Ami60JPPrdq5oFPc6TjmL9klZ6W+gBvfkx0=";
+
+  buildInputs = [ brotli p7zip ];
+
+  # The tests requires the package itself to be installed and IDK how to do it.
+  doCheck = false;
+
+  meta = with lib; {
+    description = "Command-line itch.io helper";
+    homepage = "https://github.com/itchio/butler";
+    license = licenses.mit;
+  };
+}

pkgs/default.nix

@@ -30,6 +30,7 @@ let
             sha256 = "sha256-lgt69FhXANsP3VuENVThHiVk/tngYfWR+uiKe+ZEb6M=";
           };
         });
+      butler = callPackage ./butler.nix { };
       devdocs-desktop = callPackage ./devdocs-desktop.nix { };
       doggo = callPackage ./doggo.nix { };
       gnome-search-provider-browser-tabs = callPackage ./gnome-search-provider-browser-tabs.nix { };