Broker need restart after making change to emq_auth_psql.conf

Here is the case:
Running Broker for the first time,
Changing emq_auth_psql.conf to suit my database credentials
load module failed because the broker didn't read the new emq_auth_psql.conf it still use the default credentials 'root' with an empty password
Solution: restart broker and it will take the new emq_auth_psql.conf

Someone has mentioned this before [#61](https://github.com/emqx/emqx-auth-pgsql/issues/61)
I posted it here so new user like me know about it
You should mention this in the online doc