It's been a long time, but I think when you launch the game you get a pop-up window. There's an option there to upload a map. Before you click launch game.

Hello,
I hava always try to put somes maps from a gerrmany death site Cos theses one are fabulous...
honestly , that was only To let people know theses wonderfull maps...
And i never think to say that i am the creator quite the contrary....
Anyways , i was unable to send any maps on the worshop....

hello. I also have posted some maps with description and image but although they upload they stay in "only friends" view mode.