Add actionable help message for --features

Fix #8770

Author: pickfire

src/cargo/util/command_prelude.rs

@@ -308,7 +308,8 @@ pub trait ArgMatchesExt {
                 if self._is_present(flag) {
                     bail!(
                         "--{} is not allowed in the root of a virtual workspace\n\
-                         note: while this was previously accepted, it didn't actually do anything",
+                         note: while this was previously accepted, it didn't actually do anything\n\
+                         help: try cd into the package and run cargo command",
                         flag
                     );
                 }