update the warning on as_command_mut

Author: Shourya742

src/bootstrap/src/utils/exec.rs

@@ -203,8 +203,9 @@ impl<'a> BootstrapCommand {
     /// Provides access to the stdlib Command inside.
     /// FIXME: This function should be eventually removed from bootstrap.
     pub fn as_command_mut(&mut self) -> &mut Command {
-        // We don't know what will happen with the returned command, so we need to mark this
-        // command as executed proactively.
+        // We proactively mark this command as executed since we can't be certain how the returned
+        // command will be handled. Caching must also be avoided here, as the inner command could be
+        // modified externally without us being aware.
         self.mark_as_executed();
         self.cache_never();
         &mut self.command