Adds surface properties to the game's physics environment.
The game has a limit of 128 surface properties - this includes properties loaded automatically from surfaceproperties.txt. Due to this, there's only a small amount of open slots that can be registered with GMod's provided surfaceproperties.txt.
1 string properties
The properties to add. Each one should include "base" or the game will crash due to some values being missing.
Adds the "" surface property from TF2.