Add new endpoints to "Breaking changes" section on upgrade-notes.ascii

docs/upgrade-notes.asciidoc

@@ -54,13 +54,34 @@ For Elastic Security solution release information, refer to {security-guide}/rel
 [%collapsible]
 ====
 *Details* +
-ADD MORE DETAILS ON WHAT IS CHANGING AND A LINK TO THE PR INTRODUCING THE CHANGE
+--
+* `POST /api/detection_engine/rules/_bulk_create` has been replaced by `POST /api/detection_engine/rules/_import`
+* `PUT /api/detection_engine/rules/_bulk_update` has been replaced by `POST /api/detection_engine/rules/_bulk_action`
+* `PATCH /api/detection_engine/rules/_bulk_update has been replaced by `POST /api/detection_engine/rules/_bulk_action`
+* `DELETE /api/detection_engine/rules/_bulk_delete` has been replaced by `POST /api/detection_engine/rules/_bulk_action`
+* `POST api/detection_engine/rules/_bulk_delete` has been replaced by `POST /api/detection_engine/rules/_bulk_action`
+--
+These changes were introduced in PR {kibana-pull}#197422[#197422].
 
 *Impact* +
-ADD INFORMATION ABOUT WHAT THIS CHANGE WILL BREAK FOR USERS
+Deprecated endpoints will fail with a 404 status code starting from version 9.0.0
 
 *Action* +
-ADD INSTRUCTIONS FOR USERS LOOKING TO UPGRADE. HOW CAN THEY WORK AROUND THIS?
+--
+Update your implementations to use the new endpoints:
+
+1. **For bulk creation of rules:**
+   - Use `POST /api/detection_engine/rules/_import` (link:https://www.elastic.co/docs/api/doc/kibana/v8/operation/operation-importrules[API documentation]) to create multiple rules along with their associated entities (e.g., exceptions and action connectors).
+   - Alternatively, create rules individually using `POST /api/detection_engine/rules` (link:https://www.elastic.co/docs/api/doc/kibana/v8/operation/operation-createrule[API documentation]).
+
+2. **For bulk updates of rules:**
+   - Use `POST /api/detection_engine/rules/_bulk_action` (link:https://www.elastic.co/docs/api/doc/kibana/v8/operation/operation-bulkaction[API documentation]) to update fields in multiple rules simultaneously.
+   - Alternatively, update rules individually using `PUT /api/detection_engine/rules` (link:https://www.elastic.co/docs/api/doc/kibana/v8/operation/operation-updaterule[API documentation]).
+
+3. **For bulk deletion of rules:**
+   - Use `POST /api/detection_engine/rules/_bulk_action` (link:https://www.elastic.co/docs/api/doc/kibana/v8/operation/operation-performrulesbulkaction[API documentation]) to delete multiple rules by IDs or query.
+   - Alternatively, delete rules individually using `DELETE /api/detection_engine/rules/{id}` (link:https://www.elastic.co/docs/api/doc/kibana/v8/operation/operation-deleterule[API documentation]).
+--
 ====