Add "whey" under "Packaging"

[domdfcoding]

Resource description

whey is a PEP 517 build backend using PEP 621 metadata defined in pyproject.toml to build wheels and source distributions. It can also be called directly.

By submitting this pull request I confirm I've read and complied with the below requirements

• [X] I have read and understood the Contribution Guidelines
• [X] I am making an individual pull request for each entry
• [X] I have added a useful title to the commit
• [X] I have added a useful title to this PR
• [X] I have added the new entry in alphabetical order
• [X] I have used the following format:

  - [Resource Title](link) - Resource short Description (2 lines or less in total)
  

• [X] The new entry meets one of these categories:
  • Is configured via its own tool sub-table in the pyproject.toml file (i.e., [tool.xxx])
  • Is a project template using the pyproject.toml file
  • Is an article about the pyproject.toml file
  • Is a link to a project discussion about pyproject.toml support

[carlosperate]

Thanks to the contribution @domdfcoding! It's still a bit early for the project, but looks very promising. Let's wait a bit until it gains more traction.