Info about SubmitGJUserInfo.php

[KoLeS2109]

restoreGJItems.php is associated with submitGJUserInfo.php, but there is no information about this file

[Wyliemaster]

Since its no longer used in 2.1, other things have talen priority. Still needs documenting though. Thanks for bringing it up

[idkreally-3537]

This is solved in pull request #116