Add explanatory tooltip to "Add to stacks" button

I love the new "Add to stacks" feature! It's amazing! Playing similar games previously, this has been a significant QoL improvement. But for some new players, this concept might be hard to grasp. A "stack" is not the most common concept, and might not be intuitively understood by all players. I would suggest adding adding a tooltip to the button explaining the mechanics of what's going to happen. *Concrete suggestion: Add tooltip to "Add to stacks" button that explains the mechanics of adding items of the same kind from your inventory to the container's inventory.* _Note: This seems like a low-hanging fruit, but that's dependent on this not requiring you to rewrite the entire button-mechanic. I haven't seen any other buttons with tooltips in Icarus, so this leads me to believe that the hover-mechanic hasn't been implemented (or utilized) previously for this entity._ _Feel free to contact me for follow-up questions, if relevant!_