Add PostgreSQL Adapter.

Author: hsluoyz

README.md

@@ -155,6 +155,7 @@ Adapter | Type | Author | Description
 [Redis Adapter](https://github.com/ankitm123/redis-adapter) | KV store | [@ankitm123](https://github.com/ankitm123) | Persistence for [Redis](https://redis.io/)
 [Protobuf Adapter](https://github.com/casbin/protobuf-adapter) | Stream | Casbin | Persistence for [Google Protocol Buffers](https://developers.google.com/protocol-buffers/)
 [RQLite Adapter](https://github.com/edomosystems/rqlite-adapter) | SQL | [EDOMO Systems](https://github.com/edomosystems) | Persistence for [RQLite](https://github.com/rqlite/rqlite/)
+[PostgreSQL Adapter](https://github.com/going/casbin-postgres-adaptor) | SQL | [Going](https://github.com/going) | Persistence for [PostgreSQL](https://www.postgresql.org/)
 
 For details of adapters, please refer to the documentation: https://github.com/casbin/casbin/wiki/Policy-persistence