Hands-On Rust: Explain Read<xxx> introduced at end of chapter 7

Title: Hands-On Rust (End of chapter 7)

the query to acquire movers is changed to add Entity (that seems obvious), but point was changed from &mut Point to Read<Point>. ( I understand it’s not necessary to be mutable anymore), and &MovingRandomly is changed to Read<MovingRandomly>.

I don’t recall seeing the Read<xxx> stuff before and think it could use elaboration here.