How To Backup Garry's Mod Workshop Addons (.GMA)

FINAL UPDATE:
A newer video on this topic has been created. It does not negate or nullify this video, but it provides alternative routes you can take to backup your addons. Apologies if it feels rushed in places, I spent the whole day on it but that doesn't change the fact that it is, in fact, a bit rushed.
• How To Backup and Extr...
Made this really quickly in light of recent events, to help out some friends. You might need to launch GMOD for some addon names to update, but that should be the only thing I forgot to mention. I can make a video on extracting .GMAs later.