home: vim: configure 'null-ls' for 'nix'

home/vim/after/ftplugin/nix.vim

@@ -0,0 +1,10 @@
+" Create the `b:undo_ftplugin` variable if it doesn't exist
+call ftplugined#check_undo_ft()
+
+" Set-up LSP, linters, formatters
+lua << EOF
+local null_ls = require("null-ls")
+null_ls.register({
+    null_ls.builtins.formatting.nixpkgs_fmt,
+})
+EOF