docs: update limitations

README.md

@@ -130,10 +130,16 @@ the Pico architecture:
   - [Observability](./docs/deploy/observability.md)
 
 ## Limitations
-> :warning: Pico is still a proof of concept so is not yet suitable for
-production.
+> :warning: Pico not suitable for production.
+
+Pico is currently a proof of concept.
+
+It supports tunnelling with a single Pico server node, though doesn't yet
+support clustering or authentication.
 
-Pico does not yet support clustering or authentication.
+The next step is to add clustering support, where both upstream listeners and
+downstream clients can connect to any node in the cluster (via a load balancer)
+and Pico handles routing requests between the two.
 
 Pico also only supports using Pico agent to register listeners, though aiming
 to add support for a Go SDK as well.