Fix wrong reference to AsyncConsumer in Introduction

[DanielSwain]

Change AsyncConsumer to AsyncWebsocketConsumer

[carltongibson]

Hi @DanielSwain.

Is this right? Subclassing AsyncWebsocketConsumer you'd implement receive() rather than override the websocket_connect() and websocket_receive() methods, which are implemented for you, and are the benefit of using the generic consumer... 🤔

[DanielSwain]

@carltongibson Perhaps. I only traced the AsyncConsumer definition in the code and saw that it didn't have function definitions for either websocket_connect() or websocket_receive() and so figured that the author of the docs intended AsyncConsumer to be AsyncWebsocketConsumer since websocket_connect() and websocket_receive() were specifically overridden in the example provided. With what you're saying, however, perhaps that assumption is backwards. It seems that there is definitely an error in the docs here, so I'll let it to you or the original document writer (if not you) to take it from here.