router.post("/addtodo", async (req, res) => {
    try {
      const updateUser = await User.updateOne(
        {
          _id: req.body._id
        },
        {
          $push: {
            todos: { title: req.body.title }
          }
        }
      );
      res.send("you added new todo");
    } catch (error) {
      res.send("Error");
    }
  });