added permission

Signed-off-by: ashwinkumar12345 <kumarjao@users.noreply.github.com>

_monitoring-plugins/ad/index.md

@@ -54,6 +54,7 @@ A detector is an individual anomaly detection task. You can define multiple dete
    - To use the custom result index option, you need the following permissions:
       - `indices:admin/create` - If the custom index already exists, you don't need this.
       - `indices:data/write/index` - You need the `write` permission for the anomaly detection plugin to write results into the custom index for a single-entity detector.
+      - `indices:data/read/search` - You need the `search` permission because the anomaly detection plugin needs to search custom result indices to show results on the anomaly detection UI.
       - `indices:data/write/delete` - Because the detector might generate a large number of anomaly results, you need the `delete` permission to delete old data and save disk space.
       - `indices:data/write/bulk*` -  You need the `bulk*` permission because the anomaly detection plugin uses the bulk API to write results into the custom index.
    - Managing the custom result index: