submitGJUserInfo.php is not documented

[idkreally-3537]

submitGJUserInfo.php is a file that's used in the "restore" functionality before the current save system was implemented. You can't make the server process the data anymore, but it's still found in both the game's code and on the servers. As far as I know it's not documented anywhere. I've made a pull request #116 that adds documentation for it as well as fixing the GJP issue (which several previous issues have adressed)