Update documentation about the delete command

README.md

@@ -232,6 +232,14 @@ The app exposes the following [gRPC](https://grpc.io/) services :
     -   waypoints: an array of addresses that represent the waypoints of the journey (only first and last waypoints are used for passenger ads). Note that positions are **required** and **must** be consecutives
     -   comment: optional freetext comment / description about the ad
 
+-   **Delete** : Delete permanently an ad
+
+    ```json
+    {
+        "id": "80126a61-d128-4f96-afdb-92e33c75a3e1"
+    }
+    ```
+
 ## Messages
 
 ### Handled