Add an example of reacting to incoming data

> A use case I see is flagging vaccine shortage at facility supportive supervision and emailing facility focal person on which vaccine has stocked out

The issue names no file, test, or entry point. Start by reviewing the repository's existing examples and documentation for handling incoming data, then identify where a new example belongs. Done means documenting a vaccine-stockout use case that shows reacting to incoming data and emailing the facility focal person.

Written by the indexing model from the issue text.