wireless-bridge.sh: add script

This script twiddles the firewall settings so that the computer on which it is
run will act as a bridge between wifi and wired networks.

This computer:
	- wifi to internet
	- wired networking to hub and computers behind it (on hub)

To connect the computers from the hub to the internet, run this script (check
settings) as root.

Signed-off-by: Trevor Woerner <twoerner@gmail.com>