Add failed_pipeline and success_pipeline to API doc

Feedback:
https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/6342#note_17981448

doc/api/notification_settings.md

@@ -79,6 +79,8 @@ curl --request PUT --header "PRIVATE-TOKEN: 9koXpg98eAheJpvBs5tK" https://gitlab
 | `close_merge_request` | boolean | no | Enable/disable this notification |
 | `reassign_merge_request` | boolean | no | Enable/disable this notification |
 | `merge_merge_request` | boolean | no | Enable/disable this notification |
+| `failed_pipeline` | boolean | no | Enable/disable this notification |
+| `success_pipeline` | boolean | no | Enable/disable this notification |
 Example response:
@@ -143,6 +145,8 @@ curl --request PUT --header "PRIVATE-TOKEN: 9koXpg98eAheJpvBs5tK" https://gitlab
 | `close_merge_request` | boolean | no | Enable/disable this notification |
 | `reassign_merge_request` | boolean | no | Enable/disable this notification |
 | `merge_merge_request` | boolean | no | Enable/disable this notification |
+| `failed_pipeline` | boolean | no | Enable/disable this notification |
+| `success_pipeline` | boolean | no | Enable/disable this notification |
 Example responses:
@@ -163,7 +167,9 @@ Example responses:
     "reopen_merge_request": false,
     "close_merge_request": false,
     "reassign_merge_request": false,
-    "merge_merge_request": false
+    "merge_merge_request": false,
+    "failed_pipeline": false,
+    "success_pipeline": false
   }
 }
 ```