move the ReactNativeFeatureFlags outside of sync dir

Reviewed By: bvaughn

Differential Revision: D5627037

fbshipit-source-id: 0544b822ba03090a74695911b6951e91262478a0

Libraries/ReactNative/ReactNativeFeatureFlags.js

@@ -12,6 +12,11 @@
 
 'use strict';
 
+// =============================================================================
+// IMPORTANT:
+// When syncing React Renderer, make sure the feature flags are still compatible
+// =============================================================================
+
 var useFiber;
 
 var ReactNativeFeatureFlags = {