add option to use change folding mode (#978)

lua/default-config.lua

@@ -20,6 +20,8 @@ O = {
     completeopt = { "menuone", "noselect" },
     conceallevel = 0, -- so that `` is visible in markdown files
     fileencoding = "utf-8", -- the encoding written to a file
+    foldmethod = "manual", -- folding, set to "expr" for treesitter based foloding
+    foldexpr = "", -- set to "nvim_treesitter#foldexpr()" for treesitter based folding
     guifont = "monospace:h17", -- the font used in graphical neovim applications
     hidden = true, -- required to keep multiple buffers and open multiple buffers
     hlsearch = true, -- highlight all matches on previous search pattern