Close method of WebSocketPeer not properly documented for clean close

I could be misreading the C++, but it seems in `modules/websocket/websocket_server.cpp`, online 146, if you are using the multiplayer API, then you need to be listening to the signal `peer_disconnected` instead of `client_disconnected` like the documentation says.

Change the statement:
```
Note: To achieve a clean close, you will need to keep polling until either WebSocketClient.connection_closed or WebSocketServer.client_disconnected is received.
```
to something like:
```
Note: To achieve a clean close, you will need to keep polling until either WebSocketClient.connection_closed or WebSocketServer.client_disconnected is received. If you
are using the high level multiplayer API, listen to the `peer_disconnected` signal instead.
```