Update cloud_sql/postgres/pdo/README.md
Update cloud_sql/postgres/pdo/README.md

Co-authored-by: Kurtis Van Gent <dbdae6c357ede9a5d333d52f7521158034e34b9f@users.noreply.github.com>
GoogleCloudPlatform/php-docs-samples,GoogleCloudPlatform/php-docs-samples,GoogleCloudPlatform/php-docs-samples,GoogleCloudPlatform/php-docs-samples,GoogleCloudPlatform/php-docs-samples