Better documentation for doors

[spacek531]

I'm busy making doors so I don't have time to compile this into wiki format currently.

To make the door split between left and right, add an object to mask the background of the object, which is drawn behind an incoming vehicle. Set the object's pass index to 1. Give the object a material with the following options:

• shadeless on
• transparency on
• Z transparency mode
• alpha 0
• traceable off
• use mist off
• pass index set to what color you want the background remap to be