Command for getting rules of the game

[binali-rustamov]

Often new users have problems with rules of the game.
To prevent this in the future we should provide rules for the game.

1. We should write the game rules.
2. The bot should provide these rules when a user types '/rules' in private chat.
3. From (2) this command will work only for private chats with the user.

Rules should be loaded from a file, this file can be a part of the project. It's required to format rules with markdown/HTML syntax, following these instructions: https://core.telegram.org/bots/api#formatting-options