Add DEVELOPMENT.md

DEVELOPMENT.md

@@ -0,0 +1,14 @@
+This project contains two packages, `/pkg/nats` being the current primary implementation.  This supports JetStream
+(default) and also some messaging use cases with core NATS but those aren't a perfect fit for watermill due
+to fire and forget nature of the system - acks and nacks for example are implemented as no-ops in that mode.
+However if you accept the limitations it does open up some interesting options, for example a system with
+publishers that don't require confirmation could use the core NATS mode but send to subjects included in JetStream
+subscriptions.  This lies far enough outside the streaming use cases of watermill that its included in an
+experimental fashion only but should work if resources are provisioned correctly.  It can be nice to use watermill
+as the sole interface to NATS in such a system if eg request/reply is not needed.
+
+There is also an experimental `/pkg/jetstream` package that tracks with the experimental upstream
+[JetStream API](https://github.com/nats-io/nats.go/blob/main/jetstream/README.md).  This is targeted for a
+stable API within watermill by v2.1 of this package.  Right now it only supports a very minimal configuration
+subset but does make an effort to preserve lower level access to the underlying stream provisioning API.  You can
+see an example [here](./_examples/jetstream_new.go).