Даже в скрине написано же:
https://bundler.io/guides/creating_gem.html
CODE_OF_CONDUCT.md: Provides a code of conduct that you expect all contributors to your gem to follow. Will only be included if you chose to have it included.
Примеры таких кодексов:
https://github.com/rubygems/rubygems/blob/master/C...
https://github.com/sass/sassc-ruby/blob/master/COD...
Вот тут на русском:
https://github.com/avajs/ava-docs/blob/master/ru_R... 
