enhancement: hint that threads hinder vision impared gophers

@theckman asked around and found that threads are a challenging UX for screen reader users.
Gopher could respond in threads, something like:

Hi, I noticed you posted a thread. Vision impaired gophers are likely to miss the content because it's difficult to navigate threads with screen readers. Please post in <channel> if this conversation is relevant to other gophers.

[theckman]

Would you mind re-raising this against https://github.com/gobridge/gopherbot for consideration? I'm going to be archiving this repo.