Sorry for late reply @bill.h.tucker_slack this was explained in the book. If you've used newest luminus template then you should've gotten file named dev-config.edn where you can put

{:dev true
 :port 3000
 ;; when :nrepl-port is set the application starts the nREPL server on load
 :nrepl-port 7000

 ; set your dev database connection URL here
  :database-url ""
}