doc: which events are proxied through `createWebSocketStream`

[coolaj86]

The documentation doesn't specify how the ws module stream maps to which type of Node Duplex Stream.

I assume that it behaves like a TCP Duplex Stream: https://nodejs.org/api/net.html#class-netsocket.

I also assume that the ping and pong and keepalive timeouts are proxied in a meaningful way.