Add Operators to documentation

Hi,

Thanks for this great plugin, it’s exactly what i was looking for and the code it pretty clean!
One of my requirement was to be able to filter by a custom taxonomy value OR another value. While looking at the doc and settings, i could not find anything regarding a OR statement, and the behavior default to AND.
Once i stepped into the code i saw that the plugin actually supports a operators attribute allowing this behavior.
It would be awesome if you could add this to the docs so people don’t dismiss this plugin because of this important feature seems to be missing but is actually implemented.

Have a great day