Lunch & Learn: Add section to docs on cancellation procedures

[BekahHW]

@Virtual-Coffee/maintainers I don't think I had this documented anywhere bc it usually wasn't an issue, but it would be nice to have a clear process documented for this. As part of this, we should make sure there's a clear path of communication for who to contact and how to contact them.

Should it be email, slack, google calendar invite? How soon will the project lead respond? Does it get kicked back to the process for scheduling a new brownbag? Then we can link to those docs.