Update README.md (#296)

Updated access method name in FAQ section

README.md

@@ -185,4 +185,4 @@ Date:   Wed Sep 13 09:48:31 2023 +0530
 
 ### What would be the best way to encrypt an existing table using pg_tde?
 
-- That can be done by using the ALTER TABLE command and changing the table's access method to pg_tde_basic. `ALTER TABLE table_name SET access method  pg_tde_basic;` This command rewrites the table, so for large tables, it might take a considerable amount of time. Unfortunately, rewriting the table is currently the only available option.
+- That can be done by using the ALTER TABLE command and changing the table's access method to tde_heap_basic. `ALTER TABLE table_name SET access method  tde_heap_basic;` This command rewrites the table, so for large tables, it might take a considerable amount of time. Unfortunately, rewriting the table is currently the only available option.