Ditch psql "POSTGRES_PORT_*" environment variables

postgres/content.md

@@ -30,7 +30,16 @@ $ docker run --name some-app --link some-postgres:postgres -d application-that-u
 ## ... or via `psql`
 
 ```console
-$ docker run -it --link some-postgres:postgres --rm postgres sh -c 'exec psql -h "$POSTGRES_PORT_5432_TCP_ADDR" -p "$POSTGRES_PORT_5432_TCP_PORT" -U postgres'
+$ docker run -it --rm --link some-postgres:postgres postgres psql -h postgres -U postgres
+psql (9.5.0)
+Type "help" for help.
+
+postgres=# SELECT 1;
+ ?column? 
+----------
+        1
+(1 row)
+
 ```
 
 ## Environment Variables