Folderinfo.bns

folderinfo.bns is a script file.

You can find one inside the scripts/challenges and scripts/advanced_chambers folders in portal_content.gcf

It's a pretty useful file if you want to make/customize your own BonusMap package.

Script sample

"Package_Name"
{
	"image"		"Folder_Name/TextureName"
	"comment"	"This map pack is the best one"
	"lock"		"0"
}

Package_Name : the name of your package, that's will be displayed on the bonus map selection menu with 'Challange' and 'Advanced'
image : A path to a thumbnail thats represent your package. Path is materials/vgui/FolderName/TextureName Where TextureName is the name of the .VMT file. If you leave this value empty, a default folder picture will be used.
comment : a comment about your map pack.
lock : Should be 0 to unlock your mappack, if you set it to 1 nobody can play it until it is unlocked using point bonusmaps accessor or by script editing.

How to use

The best way is to make a new folder inside your portal/maps folder like : portal/maps/MyBonusMapPack.
Put your folderinfo.bns inside it with your bonus map script and/or challenge scripts files.
You can put your map files (.bsp) in it if you want, because you can find them at a different location by using the bonus map script or challenge scripts.