Custom notification email text

Request from a user:

> Would it be possible to add some free text indicating for instance the purpose of the meeting and some details

Another option is to include a full-fledged email template editor, depending on the time we can spend on this.

The issue names no files, tests, or entry points. Start by locating the notification-email entry point, then clarify whether the requested scope is free text or a full template editor; done requires an agreed scope and customized notification email text.

Written by the indexing model from the issue text.