Add local tooling and CI wiring without bloating flake.nix

dev/flake.nix

@@ -0,0 +1,13 @@
+{
+  description = "Dependencies for development purposes";
+
+  inputs = {
+    # Flakes don't give us a good way to depend on .., so we don't.
+    # This has drastic consequences of course.
+    nixpkgs.url = "github:hercules-ci/nixpkgs/functionTo-properly";
+  };
+
+  outputs = { self, ... }:
+  {
+  };
+}