update doc comment

tokio/src/process/mod.rs

@@ -331,6 +331,9 @@ impl Command {
     }
 
     /// Cheaply convert into a `std::process::Command`.
+    ///
+    /// Note that Tokio specific options (currently only option [kill_on_drop](Command::kill_on_drop))
+    /// will be lost.
     pub fn into_std(self) -> StdCommand {
         self.std
     }