Auto-invite new members into the appropriate #general

[patcon]

We currently have #general (untranslated), #general-en, #general-ja, and #general-ko. In the future, we might be able to have arbitrary channels set up automatically by creating through Slack interface.

We can get locale from a user:
https://api.slack.com/methods/users.info/test

So we could easily check the locale of newly joined users, and either 1) auto-invite them to the appropriate #general or 2) send them a list of channels in their language, with instructions on creating ones in their language.

[patcon]

Seems that language is pretty much universally set to "en-US", so we're going to need to intuit this from "tz"