#4 README.md: clarify where translations come from

README.md

@@ -5,7 +5,10 @@ English during the initial installation before you decided to switch to another
 language (or before improving/updating the translation files).
 
 In short, it will update most CiviCRM option group and option value titles,
-as well as profiles, by attempting to translate the strings.
+as well as profiles, by attempting to translate the strings (using the CiviCRM
+core translation files, assuming they have been installed, see
+[uplang](https://civicrm.org/extensions/update-language-files) for help with
+that process).
 
 IMPORTANT: You cannot revert the process. If you want to switch back to English
 afterwards, you will have to translate your configurations manually (or you could