bridge_with_irc: Tell people to subscribe their bots to the stream.
`--stream` is a Zulip stream.
`--topic` is a Zulip topic, is optionally specified, defaults to "IRC".
+IMPORTANT: Make sure the bot is subscribed to the relevant Zulip stream!!
+
Specify your Zulip API credentials and server in a ~/.zuliprc file or using the options.
Note that "_zulip" will be automatically appended to the IRC nick provided
