Add some javascript for improved UI in the new_rule.html template

This branch adds some minimal JS in the new_rule.html to do:
 - if the user selects a stock port, auto add ths to the "port" text input
 - when the user manually selects a port, reset the stock_port 

Critical feedback appreciated as my JS client side skillz are still in development :)

Also part of the request is a bit of README update to make getting started easier.