So garry decided to finally activate his Steamworks package (or it was just given to him, I'm not stalking him, I don't know) and one of the perks is an official game group!
Here are the reasons you should join it:

-Official
-Generally better than this one
-Maintained by garry himself

So yeah, join the new group at http://ad.gamersky.info/@steamcommunity.com/games/garrysmod