Move autopairs example from README to an optional plugin

lua/kickstart/plugins/autopairs.lua

@@ -0,0 +1,16 @@
+-- autopairs
+-- https://github.com/windwp/nvim-autopairs
+
+return {
+  'windwp/nvim-autopairs',
+  event = 'InsertEnter',
+  -- Optional dependency
+  dependencies = { 'hrsh7th/nvim-cmp' },
+  config = function()
+    require('nvim-autopairs').setup {}
+    -- If you want to automatically add `(` after selecting a function or method
+    local cmp_autopairs = require 'nvim-autopairs.completion.cmp'
+    local cmp = require 'cmp'
+    cmp.event:on('confirm_done', cmp_autopairs.on_confirm_done())
+  end,
+}