Add better setup instructions

[andreasots]

Currenly it's basically 'set up LRRbot and run cargo run' which is technically correct but is actually more than eris requires:

• game_per_show_data, games, quotes, shows, state and users tables from LRRbot's database (for autotopic, Twitter announcer, !live, !quote, stream up announcer)
• Twitch OAuth2 token for the bot user in the database (needed for !live)
• a Google API token for the calendar (!next[fan], autotopic)
• a Google service account key but only when the contact form spreadsheet is set
• a Twitch client ID: (!live, autotopic)
• a Discord bot secret for basically everything
• a Discord server
• Twitter API key and secret (Twitter announcer)
• a LRRbot (stream up announcer, autotopic, simple text response commands)

Maybe some stuff should be behind feature flags so it doesn't need to be set up.