message: [docs] add postgres documentation
diff: @@ -417,6 +417,16 @@ existence of a functional SqlAlchemy dialect and Python driver. Googling
  the keyword ``sqlalchemy`` in addition of a keyword that describes the
  database you want to connect to should get you to the right place.
  +PostgreSQL
  +------------
  +
  +The connection string for PostgreSQL looks like this ::
  +
  + postgresql+psycopg2://{username}:{password}@{host}:{port}/{database}
  +
  +See `psycopg2 SQLAlchemy <https://docs.sqlalchemy.org/en/13/dialects/postgresql.html#module-sqlalchemy.dialects.postgresql.psycopg2>`_.
  +
  +
  Hana
  ------------
  