Add stand-alone explanation

src/cargo/ops/cargo_clean.rs

@@ -297,7 +297,10 @@ fn rm_rf(path: &Path, config: &Config, progress: &mut dyn CleaningProgressBar) -
         let entry = entry?;
         progress.on_clean()?;
         if entry.file_type().is_dir() {
-            // `remove_dir_all` is used here due to https://github.com/rust-lang/cargo/issues/11441
+            // The contents should have been removed by now, but sometimes a race condition is hit
+            // where other files have been added by the OS. `paths::remove_dir_all` also falls back
+            // to `std::fs::remove_dir_all`, which may be more reliable than a simple walk in
+            // platform-specific edge cases.
             paths::remove_dir_all(entry.path())
                 .with_context(|| "could not remove build directory")?;
         } else {