When you find a wizard spell of 1st level or higher, you can add it to your spellbook if it is of a spell level you can prepare and if you can spare the time to decipher and copy it.
So you can copy cantrips into your spellbook too which should not be possible with RAW. Reasdon I bring that up is found a shocking grasp scroll and was able to add it to the spellbook.
You kind of get the feeling Larian views all the 5E rules as just suggestions.