Prompt new users joining channels about what they're looking for, and give them some options

[lpatmo]

Similar idea to issue #17:

• /events endpoint will listen for new joins to a channel
• Bot will ask user what they're interested in. Maybe we can prompt three default answers:
  a) Looking for help
  b) Looking for a study partner on X
  c) Willing to share knowledge/help others
  c) Lurking

If they select a), we give them some advice on how to structure their question.
If they select b), we give them a (manually curated?) list of study groups associated with the channel, and let them know they can start their own group if they want.

What do folks think of these ideas?