Added XRG

XRG is an open source system monitor for Mac OS X. XRG allows you to
monitor CPU activity, memory usage, battery status, machine
temperature, network activity, disk I/O, current weather, and stock
market data. The goal of XRG is to be a functional system monitor that
has a clean and flexible interface, so it doesn't intrude on the rest
of your Mac experience.
Merge pull request #3003 from alebcay/xrg

Added XRG