fix example in README
fix example in README

Summary:

The example has a syntax error, separating array elements with a period
instead of a comma.

Reviewed By: svmastersamurai

Differential Revision: D25909268

fbshipit-source-id: 6f35662fdbb448032f6051ca98f1f86f5e0b61e0

facebook/IT-CPE,facebook/IT-CPE,facebook/IT-CPE