It's an experimental way to calculate how "volatile" is a project source code repository, by comparing the amount of dead code (rarely touched) with the amount of actively modified one. More or less detailed theoretical summary is in theory.pdf.
You need to have Ruby 2.6+ installed. Then you install this tool:
$ gem install volatility
Then, you run it:
$ volatility --help
How to contribute
$ bundle update $ bundle exec rake
If it's clean and you don't see any error messages, submit your pull request.