Clearer README.md
Clearer README.md

Summary: Improves some of the wording to make it easier to grok

Reviewed By: zeyadsalloum

Differential Revision: D19499146

fbshipit-source-id: 3cb74b15c1d11d1d4d7149fc9b2038bb1a6f6e2e

facebook/FBSimulatorControl,facebook/FBSimulatorControl,facebook/FBSimulatorControl,facebook/FBSimulatorControl,facebook/FBSimulatorControl