This game is creative commons so you can use the content or add to it freely.
Ideally if you use the content you'd add this to it:
Some text from CairnHammer by Andrew Cavanagh
CC-BY-SA 4.0
EpicEmpires.org
If you'd like to contribute in some way just drop me a message here and we can have a chat about what might work. There are a few restrictions, not because of me or the creator of Cairn, but because of the company that owns the game that is used for this game's inspiration.