Document the need for this package

[martinheidegger]

With expo 38 the expo system brought new Notifications that are delivered directly over websocket, pretty much like this package does. That might be understood as: we will loose all the merits of this package, but that is not the case:

This package will allow us to send a lot of notifications directly through our server, rather than expo. Which creates a lower dependency and the notifications are not handled by a third party. We also might have the opportunity to switch it out for a notification system that is a little bit more "closer to the metal" for react-native without expo, in case we eject at some point. Furthermore: by having control our own solution we are in the position to experiment with truly decentralized notification systems.