Update docs: The command line options don't work

The only thing that worked was setting the port through an environment
variable.
Adds command line option to specify the port.

The port can now be given on the command line explicitly. There may
already be an environment variable named port, in use by some other app.
The command line argument will override that.
update docs: port specified on cmd overrides all

documents the now functional port argument for the command line.