improve readme

README.md

@@ -29,7 +29,7 @@ There are also proof-of-concept ports of this script that only support basic RES
 
   - PHP 7.0 or higher with PDO drivers enabled for one of these database systems:
     - MySQL 5.6 / MariaDB 10.0 or higher for spatial features in MySQL
-    - PostGIS 2.0 or higher for spatial features in PostgreSQL 9.1 or higher
+    - PostgreSQL 9.1 or higher with PostGIS 2.0 or higher for spatial features
     - SQL Server 2012 or higher (2017 for Linux support)
     - SQLite 3.16 or higher (spatial features NOT supported)