docs: clarify the workflow to ensure the changes are effective (#20099)

Signed-off-by: Tianyu Xia <tyxia@google.com>

Mirrored from https://github.com/envoyproxy/envoy @ dffddfad2db79ed01d9985da2e0de181aedfb865

STYLE.md

@@ -149,8 +149,8 @@ To add an extension config to the API, the steps below should be followed:
 1. Add a reference to the v3 extension config in (1) in [api/versioning/BUILD](versioning/BUILD) under `active_protos`.
 1. If you introduce a new extension category, you'll also need to add its name
    under `EXTENSION_CATEGORIES` in: [tools/extensions/extensions_check.py](../tools/extensions/extensions_check.py).
-1. Run `./tools/proto_format/proto_format.sh fix`. This should regenerate the `BUILD` file and
-   reformat `foobar.proto` as needed.
+1. Run `./tools/proto_format/proto_format.sh fix`. Before running the script, you will need to commit your local changes to make them effective,
+   otherwise it will skip proto_format.sh due to no API change detected. This should regenerate the `BUILD` file and reformat `foobar.proto` as needed.
 
 ## API annotations