update the example of generated postgresql config

guides/source/command_line.md

@@ -564,14 +564,20 @@ We had to create the **gitapp** directory and initialize an empty git repository
 $ cat config/database.yml
 # PostgreSQL. Versions 8.2 and up are supported.
 #
-# Install the ruby-postgres driver:
-#   gem install ruby-postgres
-# On Mac OS X:
-#   gem install ruby-postgres -- --include=/usr/local/pgsql
+# Install the pg driver:
+#   gem install pg
+# On OS X with Homebrew:
+#   gem install pg -- --with-pg-config=/usr/local/bin/pg_config
+# On OS X with MacPorts:
+#   gem install pg -- --with-pg-config=/opt/local/lib/postgresql84/bin/pg_config
 # On Windows:
-#   gem install ruby-postgres
+#   gem install pg
 #       Choose the win32 build.
 #       Install PostgreSQL and put its /bin directory on your path.
+#
+# Configure Using Gemfile
+# gem 'pg'
+#
 development:
   adapter: postgresql
   encoding: unicode