Garrysmod Loading Screen?

I want to add a picture to my Garrysmod loading screen. Just like most server has. but I don’t know how or what files to go to. I would really like some help, Thanks.

sv_loadingurl “http://www.facepunch.com/

There’s quite a nice page on it on the old wiki, features examples of both the JS and PHP sides of a fully featured loading screen http://maurits.tv/data/garrysmod/wiki/wiki.garrysmod.com/indexb59e.html