doc: Mention --experimental-top-level-await flag

Author: dfabulich

locale/en/blog/release/v14.3.0.md

@@ -22,7 +22,7 @@ including the autocompleted part. Pressing `<escape>` cancels that behavior.
 
 #### Support for Top-Level Await
 
-It's now possible to use the await keyword outside of async functions.
+It's now possible to use the await keyword outside of async functions, with the `--experimental-top-level-await` flag.
 
 #### Other Notable Changes