add nvim-ufo for folding

lua/config/ufo.lua

@@ -0,0 +1,14 @@
+ -- disable foldcolumn, see https://github.com/kevinhwang91/nvim-ufo/issues/4
+vim.o.foldcolumn = '0'
+vim.o.foldlevel = 99 -- Using ufo provider need a large value, feel free to decrease the value
+vim.o.foldlevelstart = 99
+vim.o.foldenable = true
+
+-- treesitter as a main provider instead
+-- Only depend on `nvim-treesitter/queries/filetype/folds.scm`,
+-- performance and stability are better than `foldmethod=nvim_treesitter#foldexpr()`
+require('ufo').setup({
+    provider_selector = function(bufnr, filetype, buftype)
+        return {'treesitter', 'indent'}
+    end
+})