Fix layout

Signed-off-by: Dj Walker-Morgan <dj.walker-morgan@enterprisedb.com>

Author: djw-m

product_docs/docs/pgd/6/reference/index.mdx

@@ -53,6 +53,7 @@ The PGD Reference section provides detailed information about PGD's features.
 * [Upgrades](/pgd/latest/reference/upgrades)
 
 ## Advanced Functionality
+
 * [Application Usage](/pgd/latest/reference/appusage)
   Guidance for developers wanting to use PGD's advanced functionality in their applications.
 * [DDL](/pgd/latest/reference/ddl)