So, I can just drop a .wad file into the right folder (C:\Users\MYNAME\Saved Games\id Software\DOOM Classic\WADs) but they just list as WADNAME.WAD with a generic image. I looked at the official addons and they are in subfolders (with the actual wads renamed to the folder name) along with 4 screenshots and a "metadata" file.

Presumably, this metadata file tells the game/gui what to show (hex editing it shows it indeed contains the text) and is thus what I need to add for my custom WAD... but what format is the "metadata" file in so I can write my own?!