docs: fix link and clarify postgres install instructions (apache#16101)

docs/src/pages/docs/Connecting to Databases/index.mdx

@@ -47,7 +47,7 @@ A list of some of the recommended packages.
 |[IBM Netezza Performance Server](/docs/databases/netezza)|```pip install nzalchemy```|```netezza+nzpy://<UserName>:<DBPassword>@<Database Host>/<Database Name>```|
 |[MySQL](/docs/databases/mysql)|```pip install mysqlclient```|```mysql://<UserName>:<DBPassword>@<Database Host>/<Database Name>```|
 |[Oracle](/docs/databases/oracle)|```pip install cx_Oracle```|```oracle://```|
-|[PostgreSQL](/docs/databases/postgresql)|```pip install psycopg2```|```postgresql://<UserName>:<DBPassword>@<Database Host>/<Database Name>```|
+|[PostgreSQL](/docs/databases/postgres)|```pip install psycopg2```|```postgresql://<UserName>:<DBPassword>@<Database Host>/<Database Name>```|
 |[Trino](/docs/databases/trino)|```pip install sqlalchemy-trino```|```trino://{username}:{password}@{hostname}:{port}/{catalog}```|
 |[Presto](/docs/databases/presto)|```pip install pyhive```|```presto://```|
 |[SAP Hana](/docs/databases/hana)|```pip install hdbcli sqlalchemy-hana or pip install apache-superset[hana]```|```hana://{username}:{password}@{host}:{port}```|

docs/src/pages/docs/Connecting to Databases/postgres.mdx

@@ -8,8 +8,8 @@ version: 1
 
 ## Postgres
 
-Note that the Postgres connector library [psycopg2](https://www.psycopg.org/docs/) comes out of the
-box with Superset.
+Note that, if you're using docker-compose, the Postgres connector library [psycopg2](https://www.psycopg.org/docs/)
+comes out of the box with Superset.
 
 Postgres sample connection parameters: