Update README.md

Author: sunaoka

README.md

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 # PostgreSQL Error Codes for PHP
 
+[![License](https://poser.pugx.org/sunaoka/php-postgresql-errors/license)](https://packagist.org/packages/sunaoka/php-postgresql-errors)
+[![PHP](https://img.shields.io/packagist/php-v/sunaoka/php-postgresql-errors)](composer.json)
+[![Test](https://github.com/sunaoka/php-postgresql-errors/actions/workflows/test.yml/badge.svg)](https://github.com/sunaoka/php-postgresql-errors/actions/workflows/test.yml)
+[![codecov](https://codecov.io/gh/sunaoka/php-postgresql-errors/branch/develop/graph/badge.svg)](https://codecov.io/gh/sunaoka/php-postgresql-errors)
+
+----
+
 ## Installation
 
 ```bash