Based on some research, it seems the leaves contain tannins and so I imagine some number of rounds of boiling are required to extract those/reduce them to an acceptable level. But the texture of oak leaves isn't ideal for eating based on what I remember as a kid. So I'm curious how to deal with that issue. Some type of fermentation seems necessary to break down the leaf compounds into softer/more edible compounds, and maybe even just pickling with vinegar might help? I was curious if anyone has tried this before and had success rendering oak leaves edible. 
I cannot find any internet source that recommends eating oak leaves, however treated.  The level of tannins in oak leaves isn't just bad-tasting; it's sufficiently strong to cause kidney or liver failure.  This is probably why there are extensive records of Native Americans tribes eating acorns but none of them eating oak leaves. It's dubious that any amount of soaking of oak leaves could remove sufficient tannins to render them safe.  Some recipes for Oak Leaf Wine involve soaking them for 5 days.  If that actually leached the majority of the tannins, the wine would be toxic, and there's no evidence that it is. So my overall answer is: you cannot eat them, use something else instead. 