Clarify TCP stream context operation in README

Add explanation that the example operates at the TCP stream context
(L4) rather than the HTTP application layer, highlighting its
usefulness for scenarios where application-layer processing should
be avoided.

Signed-off-by: Christof Gerber <christof.gerber1@gmail.com>

Author: SiiiTschiii

examples/envoy_tcp_routing/README.md

@@ -2,6 +2,8 @@
 
 Proxy-Wasm TCP filter that dynamically routes connections to different upstream clusters based on the source IP address.
 
+This example operates at the TCP stream context (L4) rather than the HTTP application layer, making it useful for use cases where application-layer processing should be avoided while still enabling intelligent routing decisions.
+
 This example is inspired by the [wasmerang](https://github.com/SiiiTschiii/wasmerang) project, which demonstrates advanced TCP routing patterns in Envoy/Istio/K8s using WASM filters.
 
 ### Overview