How are Steam controller mappings "provided"?

SDL Development
1

If you are running your game from Steam, the game controller mapping is automatically provided for your game.

I don’t understand the mechanism which provides mappings. What is required of me beyond this?

int n = SDL_NumJoysticks();
var gameControllers = new List<GameControllerHandle>();
for (int i = 0; i < n; i++)
{
    if (SDL_IsGameController(i))
    {
        gameControllers.Add(SDL_GameControllerOpen(i));
    }
}