Discord: a message by a channel's webhook.
channels: [discord: {Chime.Channels.Discord, to: System.fetch_env!("DISCORD_WEBHOOK_URL")}]The address is a webhook's URL: one for everyone (to:), or each
person's in their data (data.discord). It says the notifier's
discord/3 (a text, or :title, :body, :url), else the feed's
words, as an embed with the link that reads the notification. A webhook
Discord says is gone is skipped. Options: :to, :username,
:req_options.