Add info about testing metadata files

Author: RaphaelBut

README.md

@@ -123,7 +123,7 @@ If you are not using pd_token, create the payload file with the incidentID manua
     ```bash
     ./bin/cadctl investigate --payload-path payload
     ```
-
+    > If you are testing a new invesitigation using k8sclient, you need to run backplane locally and the metadata file needs to be temporarily commited to main.
 ## Documentation
 
 ### Investigations