std::io: minor documentation improvement for the Scanner

std/io/scan.jule

@@ -40,6 +40,7 @@ impl Scanner {
 
     // Returns bytes of recent scan.
     // Returned slice is mutable copy of buffer.
+    // The next [Scan] call will write into same internal allocation.
     fn Bytes(self): []byte { ret self.b }
 
     // Returns text from bytes of recent scan.