Rollup merge of #71944 - ldm0:arrordhint, r=sfackler

Add comment for `Ord` implementation for array

Corresponding to `Ord` implementation for slice. It hints new comer the rule of comparing two arrays.

src/libcore/array/mod.rs

@@ -375,6 +375,7 @@ fn ne(&self, other: &&'b mut [B]) -> bool {
     }
 }
 
+/// Implements comparison of arrays lexicographically.
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<T: Ord, const N: usize> Ord for [T; N]
 where