README.md: document deprecation of StateChange.

Signed-off-by: Krisztian Litkey <krisztian.litkey@intel.com>

Author: klihub

README.md

@@ -88,6 +88,22 @@ have requested to containers. This interface allows one to set up and enforce
 cluster- or node-wide boundary conditions for changes NRI plugins are allowed
 to make.
 
+### Deprecated Interfaces
+
+#### StateChange
+
+In the original wire protocol a single StateChange RPC call was used to multiplex
+most pod and container lifecycle events/requests on the wire. For external plugins
+this RPC call has been replaced with proper dedicated calls for each request and
+is now deprecated. For the time being, the runtime adaptation transparently falls
+back to funneling requests through StateChange for plugins compiled against older
+versions of the NRI stub package. This support will be removed in a future version
+of NRI.
+
+Note that transparent fallback is only possible for external binary plugins using
+ttRPC. Old WASM plugins compiled against an old version of NRI will fail to load
+with new versions of NRI.
+
 ### Plugin Registration
 
 Before a plugin can start receiving and processing container events, it needs