Fix typo

Author: CherkashinSergey

README.md

@@ -304,8 +304,8 @@ SELECT pgv_get('pack', 'var_text', NULL::text);
  before transaction block
 ```
 
-If you create a transactional variable after `BEGIN` or `SAVEPOINT` statements and than rollback
-to previous state - variable will not be exist:
+If you create a transactional variable after `BEGIN` or `SAVEPOINT` statements 
+and then rollback to previous state - variable will not be exist:
 
 ```sql
 BEGIN;