Documentation about REPL workflow

[tasxatzial]

Someone asked in the forums how to develop using the REPL. This issue is a pointer to that thread.

https://forum.exercism.org/t/using-your-code-file-from-within-repl-classpath-deps-edn-help-doc/15739

It might be a good idea to have some documentation on how to use the REPL. However, it's not really expected that anyone would take that approach, since plenty of editors and IDEs come with integrated REPL functionality.