Add a note about setting constants in exec benchmark.
Add a note about setting constants in exec benchmark.

ollie314/cordova-mobile-spec,polyvi/xface-mobile-spec,ollie314/cordova-mobile-spec,ollie314/cordova-mobile-spec,corimf/cordova-mobile-spec,polyvi/xface-mobile-spec,apache/cordova-mobile-spec,apache/cordova-mobile-spec,polyvi/xface-mobile-spec,corimf/cordova-mobile-spec,corimf/cordova-mobile-spec,apache/cordova-mobile-spec,corimf/cordova-mobile-spec,lorinbeer/cordova-mobile-spec,ollie314/cordova-mobile-spec,ollie314/cordova-mobile-spec,apache/cordova-mobile-spec,corimf/cordova-mobile-spec,apache/cordova-mobile-spec