Properties are not documented well

[j-windsor]

Several properties on this module are not documented well. Here are some examples in the Postgres module:

• additional_databases: no idea what valid values are for charset and collation.
• backup_configuration and additional_users: no documentation but luckily the properties are well named so I can figure it out.
• ip_configuration: Literally no idea where to start with this object. What goes in authorized_networks? All I know about it is the type list(map(string)) which could be anything. I would guess private_network is a self link to something, but is it a google_compute_network resource or something else?
• read_replicas: Really no idea where to start here either.

Please improve documentation so users don't have to fish through the implementation to determine how to set properties.