Update README.md

Author: xiaozhu36

README.md

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 Terraform module which create a PostgreSQL database based on Alibaba Cloud RDS Service.  
- terraform-provider-rds-postgres
+ terraform-alicloud-rds-postgres
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 English | [简体中文](https://github.com/terraform-alicloud-modules/terraform-alicloud-rds-postgres/blob/master/README-CN.md)