如何在discord.py上提到字符串？

import discord
from discord.ext import commands

bot = commands.Bot(command_prefix='!')

@bot.event
async def on_message(message):
    if message.content.startswith('!mention'):
        # 提到字符串
        await message.channel.send(f'{message.author.mention} Hello!')

bot.run('YOUR_BOT_TOKEN')