Needed policy and procedures

[kelle]

Here's an issue to keep track of smaller thing we may want to have policy and procedures documented for.

• Astropy Project Calendar. Who has access, what events go there, how to indicate level of openness.
• mailing lists: astropy users, astropy-dev, astropy-core-maintainers, astropy-coordinators, etc.

[pllim]

Maybe can add to https://github.com/astropy/astropy-project/blob/main/policies/permissions.md ?