Give a user a notice when sending a message disallowed by /restrict

[queengooborg]

In some of the Telegram chats I administer or own, I've had a few people complain about not being able to send messages at first. Because of the nature of these groups (mostly art sharing), our solution has been to disable /restrict mode, but some groups may not want to do this.

I think it would be a nice touch if Shieldy were to send a user a message after deleting a disallowed message during the restriction period, saying something along the lines of "You must wait X hours before you can send messages with links or images!" This should help explain to a user what's going on, and not cause them to be confused and potentially just leave a chat.

Additionally, I think mentions shouldn't count as links for /restrict, but that's another topic.

[backmeupplz]

Just add the explanation to your greeting :) mentions include mentions of other channels and things like "link in bio -> @borodutch"