Fix note block syntax

Author: jmikola

source/use-cases/product-catalog.txt

@@ -320,7 +320,7 @@ used in the filter and in the sort:
        ('details.genre', 1),
        ('details.issue_date', -1)])
 
-... note::
+.. note::
 
     The final component of the index is the sort field. This allows
     MongoDB to traverse the index in the sorted order to preclude a