Hi,
I'm an experienced Ruby and Ruby on Rails developer. I can set-up your Rails development environment and add the field you need on the model.
The gems you need for your setup will depend on the operating system you want to use in development and production. If it's Linux / Mac it will be easy. If it's Windows... it depends.
But generally speaking, I should have it ready in 1 day.
Any questions, just message me ;)