Add fallback() to autocompletion, add comments shortcut, add require

plugins

lua/kickstart/plugins/comments.lua

@@ -0,0 +1,17 @@
+return {
+  'numToStr/Comment.nvim',
+
+  config = function()
+    require('Comment').setup {
+      opleader = {
+        ---Line-comment keymap
+        line = '<leader>/',
+      },
+      toggler = {
+        line = '<leader>/',
+      },
+    }
+  end,
+
+  lazy = false,
+}