How to create a file example_user.rb in your application root directory in ROR using Sublime Text

I am currently following Michael Hartl's Rails tutorial and not quite sure where to create the new example_user.rb file (referenceed in section 4.4.5) because I am not sure what is meant by the root directory.

I understand how to create a new file using Sublime Text but I am not sure what path to place it in. My educated guess would be to place it in: project_app/config/locales since it is an .rb file.

Any suggestions under what path I should place this code?
Also, how could you accomplish this task using the command line?

Many thanks!