Update README.md

Author: frikky

README.md

@@ -35,6 +35,13 @@ With the above function as an example
 python3 app.py --standalone --action=sample_function paramname=World
 ```
 
+**PS: The following parameters are reserved, allowing you to set proper variables for testing such as local backends:**
+```
+--shuffle_url="http://custom_backend_url"
+--shuffle_authorization="auth"
+--shuffle_executionid="execution_id"
+```
+
 Example wit [Shuffle Tools+Liquid](https://github.com/Shuffle/python-apps/tree/master/shuffle-tools/1.2.0/src) and the [Shuffle Tools app and the "repeat back to me" function](https://github.com/Shuffle/python-apps/blob/678187d1198f5e8fd2072e475dbbbf858728dde8/shuffle-tools/1.2.0/src/app.py#L235)
 ```bash
 python3 app.py --standalone --action=repeat_back_to_me '--call={{ "hello" | replace: "o", "lol" }}'