Update README.md

Co-authored-by: Andrew Pogrebnoi <[email protected]>

README.md

@@ -59,6 +59,7 @@ FUNCTION pg_tde_add_key_provider_file(
 ```sql
 SELECT pg_tde_add_key_provider_file('file','/tmp/pgkeyring');
 ```
+**Note: The `File` provided is intended for development and stores the keys unencrypted in the specified data file.**
 6. Set the master key for the database using the `pg_tde_set_master_key` function.
 ```sql
 FUNCTION pg_tde_set_master_key (