How do you get the descriptions next to the items in the shop?

I was watching pro players play LoL on YouTube and on the shop instead of the usual square grid there are rectangles with the item icon followed by the name and a short simple description of what the item does. (eg. Infinity Edge - Massively enhances critical strikes) How do I turn it on? I see a lot of people use it and I want to turn it on too.
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