When you start a new game on http://multiplayerrobot.com and login with the yagmrc you will see the following UI's

Choose the file you would like to upload. In this case it's asdf.Civ5Save



But beware, currently there is a bug as described on
http://steamcommunity.com/groups/multiplayerrobot/discussions/0/35221584535632078/
that somehow leads to corrupted files when a linux client does the first move.