doc: improve README information

Signed-off-by: Gabriele Bartolini <gabriele.bartolini@enterprisedb.com>

README.md

@@ -3,15 +3,15 @@
 Maintenance scripts to generate Immutable Application Containers
 for all available PostgreSQL versions (11 to 15) to be used as
 operands with the [CloudNativePG operator](https://cloudnative-pg.io)
-for Kubernetes.
+for Kubernetes. PostgreSQL 16 beta is also available.
 
 These images are built on top of the [Official Postgres image](https://hub.docker.com/_/postgres)
 maintained by the [PostgreSQL Docker Community](https://github.com/docker-library/postgres),
 by adding the following software:
 
-- Barman Cloud
+- [Barman Cloud](https://www.pgbarman.org)
-- PGAudit
+- [PGAudit](https://github.com/pgaudit/pgaudit)
-- Postgres Failover Slots
+- [Postgres Failover Slots](https://github.com/EnterpriseDB/pg_failover_slots)
 
 Barman Cloud is distributed by EnterpriseDB under the
 [GNU GPL 3 License](https://github.com/EnterpriseDB/barman/blob/master/LICENSE).
@@ -22,6 +22,11 @@ PGAudit is distributed under the
 Postgres Failover Slots is distributed by EnterpriseDB under the
 [PostgreSQL License](https://github.com/EnterpriseDB/pg_failover_slots/blob/master/LICENSE).
 
+Licensing information of all the software included in the container images is
+in the `/usr/share/doc/*/copyright*` files.
+
+## Where to get them
+
 Images are available via
 [GitHub Container Registry](https://github.com/cloudnative-pg/postgres-containers/pkgs/container/postgresql).