POD patch to clarify which order to apply pragmas (and mention Moose)

Hi Leon

Thanks for your useful module. I ran into an issue in some existing code that used smartmatching and Moose. Adding `use experimental 'smartmatch'` appeared not to work because the `use Moose` was turning all warnings back on.  So not a bug in your code but a POD patch to help others who might hit the same issue.

Regards
Grant