Fix socket.ex docu

[ephe-meral]

MyApp.Endpoint.broadcast/2 is not generated by default by the endpoint, needs to have a 3rd parameter as well.

[ephe-meral]

Generally speaking this sample line might be misleading...
I thought it would do the things that it says in the comment, however this will only happen if the channels define a handler for this event, no?
(So it doesn't automatically disconnect anything?)

This would be useful feature though, to kick all the sockets / channels at the same time by force...

[chrismccord]

No, it does forcefully kick the multiplexed socket, i.e.
https://github.com/phoenixframework/phoenix/blob/master/lib/phoenix/transports/websocket.ex#L140-L143

Thanks!