To add types, I would like to have help from typeprof to define rbs files for current library code that's why I added both steep and typeprof to Gemfile.

This file indicates that type definition files are placed in the `sig` directory and the actual implementation files that I want to define types for are located in the `lib` directory.
Additionally, it is configured to disable type error checking so as not to raise much errors.

As a first step toward adopting rbs for this project, added type a definition for a simple method.
More type definitions will be added incrementally.

...uby versions