docs: add instructions to use TCP sockets
This changes the way that the apiserver parameter is handled. It now
uses a URL instead of a string which was the path of the unix socket.
The string representing a path is still allowed, if no scheme is present
it considers its a unix socket. I also log errors if klippy cannot bind
to a file or the IP, instead of raising an exception.
Signed-off-by: Anthony Bourguignon <contact@toniob.net>