add note on setting locale_dirs

locale_dirs defaults to locales but the guide uses locale instead. If only the steps in the guide are followed, sphinx can't find the translations

Author: OriolAbril

docs/user/guides/manage-translations-sphinx.rst

@@ -187,7 +187,10 @@ Finally, to build our documentation in Spanish(Argentina) we need to tell Sphinx
 
 .. note::
 
-   There is no need to create a new ``conf.py`` to redefine the ``language`` for the Spanish version of this documentation.
+   There is no need to create a new ``conf.py`` to redefine the ``language`` for the Spanish version of this documentation, 
+   but you need to set locale_dirs_ to ``["locale"]`` for Sphinx to find the translated content.
+   
+   .. _locale_dirs: https://www.sphinx-doc.org/en/master/usage/configuration.html#confval-locale_dirs
 
 After running this command, the Spanish(Argentina) version of your documentation will be under ``_build/html/es_AR``.