Create page with advice for writing a third party package #18496

Problem

There is low discoverability for several things that would make life easier for a third party package developer. For example, I had no idea what a trove classifier even was until it was suggested to me here mpl-extensions/mpl-interactions#25. I also didn't know that it was ok for me to try to advertise via matplolib (e.g. 3rd party packages page, @matplotlib on twitter)

Understanding copywrite can also be tricky, for example see this discourse conversation

Suggested Improvement

Create a Creating A Third Party Package page on the docs. Here's an initial list of topics I think would be helpful:

practical

• practical copyright rules
  • If it were homework and you didn't acknowledge would it be cheating?
  • If yes then .... (e..g add a comment and include a license file in ___ folder)
• point out that pytest-mpl exists
• admonish the use of matplotlib private methods
• information on how to passing through docstrings from https://discourse.matplotlib.org/t/docs-for-a-method-wrapping-a-matplotlib-method/21055
• link to, or subsume, https://colcarroll.github.io/yourplotlib/

communication

• Encourage tweeting about your package to @matplotlib
  • Link to https://github.com/matplotlib/governance/blob/master/communications_guidelines.md for full explanation
• Explain the standard for inclusion in the third-party-packages list/encourage or discourage this
• Mention the 3rd party packages section on discourse
  • Provide an example questions issue template redirecting questions there? (Mine is here)

ping @story645