update readme

README.md

@@ -9,12 +9,13 @@ CityDoctor2 is a Java program for validating CityGML files. It checks whether ce
 Use [Maven](https://maven.apache.org/) to build CityDoctor2.
 
 ```bash
+cd CityDoctorParent
 mvn install
 ```
 
 ## Usage
 
-Once built the CityDoctorValidation jar can be used to start the program.
+Once built there is a CityDoctorValidation-<version>.zip file in the target folder of the CityDoctorValidation folder in which the CityDoctorValidation jar can be used to start the program.
 
 ```bash
 java -jar CityDoctorValidation-<version>.jar -in <path-to-gml-file>.gml -config <path-to-validation-config>.yml -xmlReport <path-to-xml-output>.xml -pdfReport <path-to-pdf-output>.pdf