add benchmarking instructions

src/uu/sort/BENCHMARKING.md

@@ -69,6 +69,12 @@ Run `cargo build --release` before benchmarking after you make a change!
 
 -   Benchmark numeric sorting with hyperfine: `hyperfine "target/release/coreutils sort shuffled_numbers_si.txt -h -o output.txt"`.
 
+## External sorting
+
+Try running commands with the `-S` option set to an amount of memory to be used, such as `1M`. Additionally, you could try sorting
+huge files (ideally multiple Gigabytes) with `-S`. Creating such a large file can be achieved by running `cat shuffled_wordlist.txt | sort -R >> shuffled_wordlist.txt`
+multiple times (this will add the contents of `shuffled_wordlist.txt` to itself).
+
 ## Stdout and stdin performance
 
 Try to run the above benchmarks by piping the input through stdin (standard input) and redirect the

src/uu/sort/src/sort.rs

@@ -1169,9 +1169,7 @@ fn file_to_lines_iter<'a>(
             })
             .map(move |line| {
                 Line::new(
-                    std::str::from_utf8(&line.unwrap())
+                    crash_if_err!(1, String::from_utf8(crash_if_err!(1, line))),
-                        .expect("input is not valid utf-8")
-                        .to_string(),
                     settings,
                 )
             }),
@@ -1226,7 +1224,7 @@ fn exec(files: Vec<String>, settings: GlobalSettings) -> i32 {
                 } else {
                     b'\n'
                 }) {
-                    let string = String::from_utf8(line.unwrap()).unwrap();
+                    let string = crash_if_err!(1, String::from_utf8(crash_if_err!(1, line)));
                     lines.push(Line::new(string, &settings));
                 }
             }