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/notify.lua

@@ -0,0 +1,10 @@
+-- A fancy, configurable notification manager
+-- https://github.com/rcarriga/nvim-notify
+return {
+  "rcarriga/nvim-notify",
+  opts = {
+    render = "minimal",
+    stages = "static",
+    timeout = 2000,
+  },
+}