Update document for postgresql_default_privileges resource (#468)

Author: caodangtinh

Diff for: website/docs/r/postgresql_default_privileges.html.markdown

@@ -28,17 +28,31 @@ resource "postgresql_default_privileges" "read_only_tables" {
 
 ## Argument Reference
 
-* `role` - (Required) The name of the role to which grant default privileges on.
+* `role` - (Required) The role that will automatically be granted the specified privileges on new objects created by the owner.
 * `database` - (Required) The database to grant default privileges for this role.
-* `owner` - (Required) Role for which apply default privileges (You can change default privileges only for objects that will be created by yourself or by roles that you are a member of).
+* `owner` - (Required) Specifies the role that creates objects for which the default privileges will be applied.
 * `schema` - (Optional) The database schema to set default privileges for this role.
 * `object_type` - (Required) The PostgreSQL object type to set the default privileges on (one of: table, sequence, function, type, schema).
-* `privileges` - (Required) The list of privileges to apply as default privileges. An empty list could be provided to revoke all default privileges for this role.
+* `privileges` - (Required) List of privileges (e.g., SELECT, INSERT, UPDATE, DELETE) to grant on new objects created by the owner. An empty list could be provided to revoke all default privileges for this role.
 
 
 ## Examples
 
-Revoke default privileges for functions for "public" role:
+### Grant default privileges for tables to "current_role" role:
+
+```hcl
+resource "postgresql_default_privileges" "grant_table_privileges" {
+  database    = postgresql_database.example_db.name
+  role        = "current_role"
+  owner       = "owner_role"
+  schema      = "public"
+  object_type = "table"
+  privileges  = ["SELECT", "INSERT", "UPDATE"]
+}
+```
+Whenever the `owner_role` creates a new table in the `public` schema, the `current_role` is automatically granted SELECT, INSERT, and UPDATE privileges on that table.
+
+### Revoke default privileges for functions for "public" role:
 
 ```hcl
 resource "postgresql_default_privileges" "revoke_public" {