Made it clear that an action must be selected to create a duplicate

docs/user_manual/working_with_vector/vector_properties.rst

@@ -2977,7 +2977,7 @@ Duplicating Actions
 QGIS allows you to duplicate existing actions. To duplicate an attribute action, 
 open the vector :guilabel:`Layer Properties` dialog and click on the :guilabel:`Actions` tab. 
 In the :guilabel:`Actions` tab, click the |duplicateAction| :sup:`Duplicate an action`
-to open the :guilabel:`Duplicate Action` dialog. You must have at least one existing action 
+to open the :guilabel:`Duplicate Action` dialog. You must have selected at least one existing action 
 in order to create a duplicate.
 
 In the dialogue that appears, make any changes that are necessary. See :ref:`adding_actions`