At Kelvin's Cairn, make a menu tab accessible to read about various game mechanics such as:

Stats - e.g. explain how Elemental Penatration works.
Conditions (Status Effects) - short descriptions
Short Rest Loot Bonus
Set Gear Bonuses: e.g. All three bonuses do/don't stack.
Etc

This should be a simple list (like the Journal) that shows in a scrolling pane as needed.
Requires minimum dev/testing time and easy to modify content.