add ZenMode keymapping

lua/custom/plugins/init.lua

@@ -2,6 +2,10 @@
 --  I promise not to create any merge conflicts in this directory :)
 --
 -- See the kickstart.nvim README for more information
+vim.keymap.set("n", "<leader>zz", function()
+    require("zen-mode").toggle()
+end)
+
 return {
     "folke/zen-mode.nvim",
 }