Add a README section about library expectations

[jepler]

Here's some draft text ... [also note that this repo does not have a copy of the code of conduct, but probably should]

Expectations for library inclusion

You're interested in having your library included in the Community Bundle? Great! Here are some things to keep in mind:

• The subject matter of your library has to be compatible with the Adafruit Community Code of Conduct
• Tagged release of the library must be compatible with circuitpython-build-tools. The best way to ensure this is to use Github Actions with files like those produced by our Cookie Cutter
• If your library has a problematic release that impacts Community Bundle releases, you will do your best to resolve it in a timely manner
• If future changes to circuitpython-build-tools impact your library, you will do your best to resolve it in a timely manner (we try to keep breaking changes to a minimum, but they do happen!)

If a particular library is causing problems for distribution in the Community Bundle we may temporarily drop it or hold it at an old revision, so that we can continue making Community Bundle releases.