Fix error in the README for surveyArea geojson

The text was incorrect, it is not relative to the config file location, but to the project directory path set in the config file

Author: kaligrafy

README.md

@@ -123,7 +123,7 @@ module.exports = {
   surveyAreaGeojsonPath: 'surveyArea.geojson'
 };
 ```
-The path is relative to the survey project directory (where the configuration file is located). If this property is missing or the file is not found, territorial validation is skipped.
+The path is relative to the survey project directory (projectDirectory param in config file). If this property is missing or the file is not found, territorial validation is skipped.
 
 ### GeoJSON Specifications