Add github discussions

[pagrubel]

Al pointed github discussions out https://docs.github.com/en/discussions I'm making it an issue so we can remember to add it when we go public. Also any discussion about it is welcome.

[mcpherson]

Might even be useful for BEE_Private. We often use issues for things that don't relate to the code (design discussions, etc.). This very issue is a case in point 😉.