Update after signup wizard to encourage subscribing to repos

[schneems]

There's an after-signup flow already, but it only prompts users to set their privacy https://github.com/codetriage/CodeTriage/blob/2c618b850ecb9863ad9dfd3b552b1857bade0b44/app/controllers/users/after_signup_controller.rb.

To get people to help with issues, we need to first get them to subscribe to repositories. Instead of sending random repos, we can be a bit more clever with our suggestions

• First ask them to assign their favorite language(s)
• Once lockfile parsing is setup (Dependency parser to find repos #1686) we could prompt them to upload a lockfile
• Recommend repos based on those other two.