add null_ls for formatting

after/plugin/defaults.lua

@@ -38,4 +38,14 @@ for type, icon in pairs(signs) do
   vim.fn.sign_define(hl, { text = icon, texthl = hl, numhl = hl })
 end
 
+-- null-ls
+
+local null_ls = require("null-ls")
+
+null_ls.setup({
+  sources = {
+    null_ls.builtins.formatting.prettierd,
+  },
+})
+
 -- vim: ts=2 sts=2 sw=2 et