Update src/uu/cat/src/cat.rs

Co-authored-by: Sylvestre Ledru <sylvestre@debian.org>

Author: karlmcdowall

src/uu/cat/src/cat.rs

@@ -613,6 +613,7 @@ fn write_end<W: Write>(writer: &mut W, in_buf: &[u8], options: &OutputOptions) -
 // however, write_nonprint_to_end doesn't need to stop at \r because it will always write \r as ^M.
 // Return the number of written symbols
 fn write_to_end<W: Write>(in_buf: &[u8], writer: &mut W) -> usize {
+    // using memchr2 significantly improves performances
     match memchr2(b'\n', b'\r', in_buf) {
         Some(p) => {
             writer.write_all(&in_buf[..p]).unwrap();