correct 0x literal info (#47348)

Co-authored-by: Stefan Karpinski <[email protected]>

doc/src/manual/integers-and-floating-point-numbers.md

@@ -185,7 +185,9 @@ determining storage size of a literal. So `0x01` is a `UInt8` while `0x0001` is
 
 That allows the user to control the size.
 
-Values which cannot be stored in `UInt128` cannot be written as such literals.
+Unsigned literals (starting with `0x`) that encode integers too large to be represented as
+`UInt128` values will construct `BigInt` values instead. This is not an unsigned type but
+it is the only built-in type big enough to represent such large integer values.
 
 Binary, octal, and hexadecimal literals may be signed by a `-` immediately preceding the
 unsigned literal. They produce an unsigned integer of the same size as the unsigned literal