document credentials

README.MD

@@ -15,8 +15,16 @@ It will output three lines per test data:
 2) a scQL query
 3) a json representation of the expected outcome of the query
 
+You need a `credentials.json` file of the form:
+
+```json
+{ "uri": "uri to scql analyser", "username": "username", "password": "password"}
+```
+
 The script can also be used with the following arguments:
 
 * `--validate` can be used to validate the queries (check for errors, for instance).
 * `--localhost` to use an analyser server running locally
 * `--no-model` to generate training data without a model
+
+