docs: use correct link, use secondary example

Author: tristan-f-r

library/alloc/src/fmt.rs

@@ -278,17 +278,20 @@
 //! Hello, `     123` has 3 right-aligned characters
 //! ```
 //!
-//! When truncuating these values, Rust uses round-to-even, which may
-//! cause concern when formatting for scientific notation. For example,
+//! When truncating these values, Rust uses [round half-to-even](https://en.wikipedia.org/wiki/Rounding#Rounding_half_to_even),
+//! which is the default rounding mode in IEEE 754.
+//! For example,
 //!
 //! ```
 //! print!("{0:.1$e}", 12345, 3);
+//! print!("{0:.1$e}", 12355, 3);
 //! ```
 //!
 //! Would return:
 //!
 //! ```text
 //! 1.234e4
+//! 1.236e4
 //! ```
 //!
 //! ## Localization