feat(nix): nix and back again

I tried Nix, but it had too many downsides so I removed it.

1. Didn't like that all files are immutable and simple config changes
need a complete rebuild.
2. Setting up a new Mac didn't work as smoothly as promised. Not worth
the effort.
3. It sucked a lot to always have to type in the password twice on each
darwin-rebuild
4. It solves problems I never had.

.config/nvim/lua/plugins/barbecue.lua

@@ -0,0 +1,15 @@
+-- barbecue.nvim
+-- https://github.com/utilyre/barbecue.nvim
+return {
+  "utilyre/barbecue.nvim",
+  name = "barbecue",
+  version = "*",
+  dependencies = {
+    "SmiteshP/nvim-navic",
+    "nvim-tree/nvim-web-devicons",
+  },
+  config = function()
+    require("barbecue").setup()
+    require("barbecue.ui").toggle(true)
+  end,
+}