Enhancement: On onboarding, ask "where did you hear about us?"

[baristaGeek]

Perfect attribution is very hard. With this enhancement we can tackle this problem.

Given a user logs in for the first time to our platform
When the login is complete
They should get a modal asking "Where did you hear about us?"

• Such modal should contain "Google Search", "Reddit", "Twitter", "Email", "A Friend", and "Other" as options.
• Ideally we would store this result as an additional column on our DB so that we can latter analyze things like "users that come from X channel end up analyzing more PRs". But if it's something else that's easier to build it's fine.