Ruby on Rails Configuration - Plaid Gem

I am trying to integrate the plaid gem into one of my projects. From the docs it says to configure it as such.

http://ift.tt/1H0Y8JE

Plaid.config do |p|
  p.customer_id = 'Plaid provided customer ID here'
  p.secret = 'Plaid provided secret key here'
  p.environment_location = 'URL for the development or production environment'
end

My question is what file should I have this code? Should it go in my application.rb? config.rb? Just want to make sure I'm following convention. Thanks!