C–H⋯O interactions and stacking of water molecules between pyrimidine bases in 5‐nitro‐1‐(β‐d‐ribosyluronic acid)–uracil monohydrate [1‐(5‐nitro‐2,4‐dioxopyrimidinyl)‐β‐d‐ribofuranoic acid monohydrate]: aneutron diffraction study at 80 K