message: Fix websocket stream read documentation
diff: @@ -1183,10 +1183,10 @@ public:
  hold all the message payload bytes (which may be zero in length).
  Control frames encountered while reading frame or message data
  - are handled automatically. Pings are replied to, pongs cause
  - an outstanding call to `async_ping` to complete, and close
  - frames initiate the WebSocket close procedure. When a close
  - frame is received, this call will eventually return
  + are handled automatically. Pings are replied to automatically,
  + pongs are routed to the pong callback if the option is set,
  + and close frames initiate the WebSocket close procedure. When a
  + close frame is received, this call will eventually return
  @ref error::closed. Because of the need to handle control
  frames, these read operations can cause writes to take place.
  Despite this, calls to `async_read` and `async_read_frame`
  