signup channel should gracefully handle attempted subscribers
800-5717 (our signup/support channel) is locked down as a vouched channel, to prevent people from subscribing to it.
Right now, if people send HELLO
to the signup channel, they will get a response like:
"Sorry, invites are required..."
Without subscribing them, they should get a message like: Welcome to the Signalboost Signup channel! You can request a channel by sending us the channel name and the phone numbers of two admins, or ask us any questions about how Signalboost works.