exec/mod.rs: added reason why we sort elements with -X

see sharkdp#441 (comment)

src/exec/mod.rs

@@ -181,14 +181,20 @@ impl CommandTemplate {
             if arg.has_tokens() {
                 // A single `Tokens` is expected
                 // So we can directly consume the iterator once and for all
+
+                // It would be too expansive to collect all the paths at once, so I take
+                // only the first ones.
                 let mut first_paths = take(&mut paths, SORT_THRESHOLD);
                 has_path = !first_paths.is_empty();
 
                 if first_paths.len() < SORT_THRESHOLD {
+                    // I sort the paths because they are not too much
                     first_paths.sort();
                     CommandTemplate::add_to_cmd(&mut cmd, arg, &mut first_paths.into_iter());
                 } else {
                     CommandTemplate::add_to_cmd(&mut cmd, arg, &mut first_paths.into_iter());
+
+                    // add remaining paths
                     CommandTemplate::add_to_cmd(&mut cmd, arg, &mut paths);
                 }
             } else {