Rollup merge of rust-lang#71315 - huangjiahua:update-documentation, r=Dylan-DPC

Add example in the alternative in std::mem::transmute docs

It is safer to use `from_ne_bytes` to convert raw bytes to type like u32.  rust-lang#71187

Author: Dylan-DPC

src/libcore/intrinsics.rs

@@ -1100,6 +1100,24 @@ extern "rust-intrinsic" {
     /// Below are common applications of `transmute` which can be replaced with safer
     /// constructs.
     ///
+    /// Turning raw bytes(`&[u8]`) to `u32`, `f64`, etc.:
+    ///
+    /// ```
+    /// let raw_bytes = [0x78, 0x56, 0x34, 0x12];
+    ///
+    /// let num = unsafe {
+    ///     std::mem::transmute::<[u8; 4], u32>(raw_bytes);
+    /// };
+    ///
+    /// // use `u32::from_ne_bytes` instead
+    /// let num = u32::from_ne_bytes(raw_bytes);
+    /// // or use `u32::from_le_bytes` or `u32::from_ge_bytes` to specify the endianness
+    /// let num = u32::from_le_bytes(raw_bytes);
+    /// assert_eq!(num, 0x12345678);
+    /// let num = u32::from_be_bytes(raw_bytes);
+    /// assert_eq!(num, 0x78563412);
+    /// ```
+    ///
     /// Turning a pointer into a `usize`:
     ///
     /// ```