Many Steam games support the steam workshop. It is an easy way to share community maps and addons and is very useful for custom servers, without needing to worry about setting up FastDL. LinuxGSM adds workshop pre-configuration to game server scripts when available.
You will need a Steam API key, a collection to subscribe to (you can create one), and some config parameters in your LinuxGSM config.
resource.AddWorkshop( "1728099077" ) --Rick Roll SENT
I do not recommend putting a collection ID in this file if you are hosting a server with a large map list, this will cause players to download every map on their first connection. Instead it is recommended to put every individual workshop item except maps in this file.