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/cheatsheet.lua

@@ -0,0 +1,16 @@
+-- Searchable Cheatsheet
+-- https://github.com/sudormrfbin/cheatsheet.nvim
+return {
+  "sudormrfbin/cheatsheet.nvim",
+  dependencies = {
+    "nvim-telescope/telescope.nvim",
+    "nvim-lua/popup.nvim",
+    "nvim-lua/plenary.nvim",
+  },
+  keys = {
+    { "<leader>C", "<cmd>Cheatsheet<cr>", desc = "Cheatsheet" },
+  },
+  config = function()
+    require("cheatsheet").setup()
+  end,
+}