From Valve Developer Community
From: 
Half-Life 2: Grey
"GameInfo"
{
// This is what shows up in the 'Third Party Games' area of the Steam games list.
game "Grey"
type singleplayer_only
icon "grey"
FileSystem
{
SteamAppId 218
ToolsAppId 211
AdditionalContentID 420
SearchPaths
{
Game |gameinfo_path|.
Game C:\szarok\
/// Game episodic
Game hl2
Game ep2
}
}
}
