Fixed incorrect flag value

Author: quellish

README.md

@@ -233,7 +233,7 @@ Xcode 9.2 has experimental support for increasing the number of concurrent build
 To enable this feature, quit Xcode and enter this command in a Terminal window:
 
 ```
-$defaults write com.apple.dt.Xcode BuildSystemScheduleInherentlyParallelCommandsExclusively -bool YES
+$defaults write com.apple.dt.Xcode BuildSystemScheduleInherentlyParallelCommandsExclusively -bool NO
 ```
 
 Test wether this benefits your project. For many projects it may not make a difference, but for others the savings may be very significant.