New members recommended to join Slack channel based on geographic location

[hollomancer]

Feature

Why is this feature being added?

In order to help support our local chapters, I want to recommend new users to join their local channels, i.e. #oc-west, #sanfrancisco, etc.

What should your feature do?

When a new user joins Slack, we should find out what their zipcode is, and recommend they join their corresponding geographical channel