unityswift-Swift.h header file is generated automatically

[ashunkhs]

#import "unityswift-Swift.h" // Required
// This header file is generated automatically when Xcode build runs.

How does unityswift-Swift get generated?

am using XCode 9.2 and Swift 4.0. any step i forget ??

[SSB4455]

import "UnitySwift-Bridging-Header.h"