[nvim] add spellcheck for markdown files

private_dot_config/nvim/lua/plugins/zenmode.lua

@@ -1,7 +1,7 @@
 return {
   {
     "folke/zen-mode.nvim",
-    ft = "mail",
+    ft = { "mail", "markdown" },
     config = function()
       require("zen-mode").setup({
 
@@ -29,5 +29,5 @@ return {
     end,
   },
 
-  { "folke/twilight.nvim", ft = "mail" },
+  { "folke/twilight.nvim", ft = { "mail", "markdown" } },
 }