[idea] [improvement] add referral textcoins

[backenders-game]

I think it would be good idea to implement referral textcoin ($1-2 for each user / or $x for every N users (for example $5 text coin for every 5 users)) for inviting users to telegram quiz bot.

You can give each user who has completed quiz referral id (or simply take his unique telegram id). Then this id can be passed to bot with start command when new user comes to bot. See https://core.telegram.org/bots#deep-linking