Update documentation, add hint for new ProcessManagerException, #26

README.md

@@ -684,8 +684,15 @@ echo $response->getDuration(); # e.g. 0.0016319751739502
 
 ### "File not found." response
 
-If you're facing a `File not found.` response after issuing a request to PHP-FPM, please make sure
-the given path to the script you want to call is an absolute path / realpath.
+This response is generated by php-fpm for the preceding error `Primary script unknown` in case the requested script 
+does not exists or there are path traversals in its path like `/var/www/../run/script.php`.
+
+**This error throws a `ProcessManagerException` from library version `2.5.0` onwards.**
+
+Prior to library version `2.5.0` this error is ignored and only present as the `File not found.` response. 
+
+If you're facing the aforementioned exception or a `File not found.` response after issuing a request to php-fpm, 
+please make sure the given path to the script you want to call is an existing absolute path / realpath.
 
 ### Doesn't work