Update README.md

README.md

@@ -45,6 +45,8 @@ When using Protobuf protocol:
 
 Event callbacks are called by SDK using `await` internally, the websocket connection read loop is blocked for the time SDK waits for the callback to be executed. This means that if you need to perform long operations in callbacks consider moving the work to a separate coroutine/task to return fast and continue reading data from the websocket.
 
+The fact WebSocket read is blocked for the time we execute callbacks means that you can not call awaitable SDK APIs from callback – because SDK does not have a chance to read the reply. You will get `OperationTimeoutError` exception. The rule is the same - do the work asynchronously, for example use `asyncio.ensure_future`. 
+
 ## Run example
 
 To run [example](https://github.com/centrifugal/centrifuge-python/blob/master/example.py), first start Centrifugo with config like this: