Good point. Old games used the printed handbook or an in-game book for such information, modern games try to give such information through books, papers, letters found in-game or dialogs with NPCs.
Possible methods in 7d:
* A letter in your starting inventory warning about zombies that might run or glow.
* Books or pamphlets that have a very high chance to be found when you are low-level could talk or warn about dangerous zombies hiding in some of the houses
* starting quests could mention them and suggest caution
* the trader you visit as part of the starting quest could have dialog options with such information with the advantage that selecting shuch dialog is purely optional