nix: add default.nix and gemset.nix

Thank you, kind person who wrote this package with forks in mind.

.gitignore

@@ -65,3 +65,6 @@ yarn-debug.log
 
 # Ignore Docker option files
 docker-compose.override.yml
+
+# Ignore nix build output
+/result

default.nix

@@ -0,0 +1,11 @@
+{ pkgs ? import <nixpkgs> { } }:
+let
+  f = (path: type: ! builtins.elem (baseNameOf path) [ ".git" "node_modules" "result" ]);
+  src = builtins.filterSource f ./.;
+in
+pkgs.mastodon.override {
+  pname = "mastodon-queer-af";
+  version = "2021-08-27";
+  srcOverride = src;
+  dependenciesDir = src;
+}