If you are using the Linux version, there should be a pdf file in the documentation folder. If not you can download it from the games page, it will be under "ZI documents pack v0.95.tar.gz". Here are some:
Emerald Tablets
Reptilian
Nan Madol
Lemurian
Enki
Enlil
Thoth
Since the game is open-source, you can also open up the file hint_hub.rpy, and view the cheats starting from line 939.
