add description for active record enumerations category

[codev009]

Thanks for contributing to the Ruby Toolbox catalog! <3

Before submitting your pull request:

• If you're referencing a gem by its GitHub repository (e.g. rails/rails), please verify
  that it is not packaged as a Ruby gem. (If it is packaged as a gem, please reference it
  by its gem name instead, e.g. rails.)
• Please make sure the projects are listed in case-insensitive alphabetical order
• Make sure the CI build passes, we validate your proposed changes in the test suite :)

[colszowka]

Nice, thanks @codev009 👍