docs: Update the API style guide (#39987)

Signed-off-by: Ali Beyad <[email protected]>

Mirrored from https://github.com/envoyproxy/envoy @ e850cd5d8fe378e32e3924d0f0122066545e2ccb

Author: update-envoy[bot]

STYLE.md

@@ -43,7 +43,8 @@ In addition, the following conventions should be followed:
   messages, or fields, respectively, that are considered work in progress and are not subject to the
   threat model or the breaking change policy. This is similar to the work-in-progress/alpha tagging
   of extensions described below, but allows tagging protos that are used as part of the core API
-  as work in progress without having to break them into their own file.
+  as work in progress without having to break them into their own file. Upon removing the
+  `(xds.annotations.v3.file_status).work_in_progress` annotation, please also update the release notes.
 
 * Always use plural field names for `repeated` fields, such as `filters`.