Provide documentation for connection options

Provide additional information on connection options.

$conn = Doctrine_Manager::connection('mysql://username:password@localhost/test', 'connection 1');

just skims the surface. At least link to PDO docs. Also, what is the second parameter? I can look in API docs, but it would be helpful to have in the reference guide.

Are there any other ways to make a connection, such as through an array of parameters?