Add example configuration for non-root master.

I would like to extend the documentation for running master as non-root.

It is a bit different than the default configuration as all files are moved inside a single folder.

I had to create a new /etc/salt/master configuration file.

I tried to put this file in /etc/salt/master.d/non-root-config but I don't know why it was not used by salt and salt-key.

Please let me know if you find it useful and it requires changes.

Feel free to discard this request if you don't find it useful.

Thanks!