Set login permission for authenticator role

This was confusing when I got started with the docs. When using CREATE ROLE, the role will not have the LOGIN permission and starting the server with `postgrest postgres://authenticator@localhost:5432/mydb --anonymous anon` will result in `FATAL: role "authenticator" is not permitted to log in`. The docs should either use CREATE USER or set LOGIN when using CREATE ROLE, as I understand it.

docs/admin/security.md

@@ -60,7 +60,7 @@ for anonymous users, one for authors, and another for the authenticator,
 you would set it up like this
 
 ```sql
-CREATE ROLE authenticator NOINHERIT;
+CREATE ROLE authenticator NOINHERIT LOGIN;
 CREATE ROLE anon;
 CREATE ROLE author;