feat: setup alejandra as a formatter.

lua/plugins/conform.lua

@@ -1,6 +1,13 @@
 vim.pack.add({
   { src = "https://github.com/stevearc/conform.nvim" },
 })
+
+require("conform").setup({
+  formatters_by_ft = {
+    nix = { "alejandra" },
+  },
+})
+
 vim.api.nvim_create_user_command("Format", function(args)
   local range = nil
   if args.count ~= -1 then