Quarterly reminder to tails-project@ about sponsorship (from [misc])

We want to let all active contributors know that it’s an option to be reimbursed when attending events on behalf of Tails. Once we have publicly available doc about how it works, we’ll set up an automated reminder that points tails-project@ to it.

Parent Task: #12632

Related issues

• Related to #7763
• Blocked by #14727 (closed)

Original created by @intrigeri on 14725 (Redmine)