Added a script for building a driver which enables the TrackPoint middle click scroll.

Taken from https://bugs.launchpad.net/ubuntu/+source/xserver-xorg-input-evdev/+bug/1246683/comments/50
Make script not complain if /etc/X11/xorg.conf.d exists.
Add README section on the middle click scrolling driver.
Merge pull request #1 from ibrahima/master

Add a script to build a custom driver which enables middle click scroll with the Trackpoint/Clickpad